You can go to Craigslist to find a nanny for your baby, a dog walker for your pooch, or an aide for grandma. Or you can go to Care.com, founded in Waltham by Sheila Lirio Marcelo, a mother of two and Internet entrepreneur, where every advertisement gets vetted by a team of mothers and every would-be caregiver’s name gets run through a national criminal records database. Basic access is free, but unlimited access and background checks costs $25 for a month – a bargain for a little peace of mind.