As campers head off, siblings can be left to wonder, 'what about me?'

In every family, there is a finely tuned equilibrium in which routines become comforting, roles familiar, and responses predictable. When a child is away at overnight camp, the equilibrium is upset. The family is out of whack. When the camper returns, it can be even worse.

No one is likely to feel these transitions more than siblings left at home.

With any luck, Sparkles, an 8-month-old Bichon Maltese, will help fill the void for 9-year-old David Fishman of Sharon when brother Michael, 13, leaves later this month for Camp Avodah in Middleborough.

This will be David's third season without his brother. The first was hard, and last year wasn't much easier. ''He would say things like, 'I miss my brother. How many days till he comes home?' " says Roberta, their mother. It was a long month, punctuated by plaintive letters from David to Michael in which he shared every little life experience (''Today I had cotton candy.") and sporadic responses from Michael (''Cool. Love you.").

When Michael came home, the brotherly reunion was decidedly one-sided. David was joyous, Michael melancholy. ''Michael missed camp," Roberta says. ''David was annoyed and frustrated. He'd tell me, 'Michael isn't talking to me. He doesn't want anything to do with me.' "

When a camper leaves, siblings can experience a range of feelings, from relief to grief. Unable to express or even identify them, children's feelings typically come out in behavior that varies by age. The preschooler is uncharacteristically clingy and whiny because the house feels empty and scary; the 6-year-old may be unusually oppositional because the sibling isn't there to serve as a foil; the 8-year-old may be alternately sad because she misses her playmate and angry because she isn't old enough to go to camp yet.

The more parents can label emotions, the sooner they'll dissipate: ''Gee, the house seems different to me without your brother. Have you noticed that?" The behaviors also are likely to disappear on their own. It doesn't take long for a child to realize he has more access to Mom or Dad, which translates to attention, almost always desirable unless parents are intrusive. When several children remain at home, the change in pecking order can free them to explore new roles in the family and relationships with each other.

Some children may come to enjoy this time so much that having the camper gone is a relief. They stop missing him altogether and then feel guilty: ''I'm a bad person. I don't want my brother to come home."

''Put this on the table," suggests Los Angeles clinical child psychologist Robin S. Cohen, a specialist in couples and family dynamics: ''Kids can have all kinds of different feelings about a sister being at camp. They might miss her more than they thought, or they might not miss her at all. Either way is OK."

Parent educator Nancy Samalin of New York City, author of ''Loving Your Child Is Not Enough" (Penguin), dismisses the idea that you can spoil a child left at home by spending a lot of time together doing something fun. If anything, she says, the time you spend alone together will provide lasting memories and a chance for a child to grow. ''Most kids thrive during this time."

Roberta Fishman looks forward to this as a time when she and David really click. ''We take long walks together. In Michael's absence, David talks to me about things he would normally share with his brother."

Of course, no sooner does your smaller family settle into a new equilibrium then it's time for the camper to return.

Chicago-area child psychologist Mark L. Goldstein, a specialist in family relationships, says there was always a week or so of unpleasantness when his son came home, although Jonathan went to camp for six summers. ''The return never got easier for him," he says. ''What made it bearable for us was learning to be flexible."

What parents typically hear from the camper is a variation on a theme: ''I didn't have to do that in camp."

When you react to this as a challenge or a test (''Get over it, this isn't camp!"), it only makes matters worse, including for the siblings on the sidelines. Your child doesn't want to shower or brush her teeth? Doesn't want to unpack, or wash her clothes? He's using language you've never heard before? ''I wouldn't get into a power struggle over any of this," Goldstein says.

That doesn't mean anything goes, rather that preemptive empathy works wonders, as well as just letting time pass. The first nights a camper is home, for instance, instead of insisting on regular bedtime, Cohen might say, ''I know you've had a lot of freedom at camp. How about some extra time at bedtime tonight?"

School psychologist Chris Thurber, coauthor of ''The Summer Camp Handbook" (Perspective Publishing), says the transition home is more complicated than parents tend to realize. For one thing, it's a total environmental change. She may be happy to return to the privacy and comfort of her own room, but feel lonely without her bunkmates. He may be happy to have air conditioning, but miss the smell of the outdoors. Thurber is also waterfront director at Camp Belknap in New Hampshire.

''They miss their friends, the routines, the autonomy, the environment," he says. ''Did I say they miss their friends?"

Cohen adds, ''They're at a stage of development where they are negotiating the issues of dependence and independence." If you're lucky, it will show itself in positive ways: She picks up after herself in the bathroom, he offers to clear the table.

More likely, it won't. ''When she says, 'Camp food was better than your cooking,' don't take it literally," advises Cohen. ''She's just playing with the idea of not needing you." Instead of reacting defensively, acknowledge that she's had some new experiences: ''Tell me what made it so good. I'd love to try something new." Enlist her help: ''Let's plan a menu together."

Fishman has come to expect Michael to be angry to be home. ''He always resents that we don't send him for the whole summer, instead of four weeks." He's also hard to communicate with. ''He comes home with all his camp-isms. We feel as if we're left out of a private joke." Luckily for everyone, Roberta and husband, Larry, were campers themselves and know that this resolves over time. ''If we try to address the specifics, it only gets worse," she says.

Siblings absolutely notice the differences. Children under 7 may be confused when a camper is sad, concluding that there's something bad about camp or bad about home. Ever egocentric, a young child may think it's her fault that her sibling is sad and go out of her way to humor or cheer up the camper, only to be met with more hostility (''Leave me alone!").

Whether they tell you about all this, Thurber suggests providing an opening: ''Everybody changes over time. Have you noticed how Josh has changed since he went to camp?" Acknowledge sadness simply: ''Your brother misses his friends at camp. He just needs a little space and time." Thurber even has a word for it: campsickness.

What you surely will hear is bickering. Sometimes there's a honeymoon period when the camper returns, but typically parents report it's as if campers bring conflict home with them. Samalin says that could just be your perspective; it's such a contrast to the peace and quiet. Or it really could be more intense. Out-of-sorts and exhausted, your camper may be picking fights. On the other hand, she says, ''For some siblings, bickering is part of the way they relate."

They're getting their equilibrium back.

Contact Barbara Meltz at meltz@globe.com.