If there’s one thing every expert agrees on, it’s that where children are concerned, one age doesn’t fit all. Kids develop at different rates, so one child might be ready to tango while another is still learning to walk. That said, there are certain kid milestones that have parents consistently curious. Here are four questions you're bound to hear at the playground, and the experts' responses to them:

When should kids start preschool?

Most preschools offer programs beginning at age two, but just because your child is 2 1/2 doesn't mean that he is ready,” says Caren Gans, Director of T’enna Preschool in Palo Alto, California. “Ask yourself the following questions: Is my child fairly independent, i.e. has he spent time away from you and can he accomplish small tasks on his own? Is he ready to participate in social situations? In other words, has he had playdates, or mommy and me experiences where he has been successful in being engaged with other children? Readiness for preschool really has less to do with age, and more to do with where your child is developmentally.”

When can kids learn to ride a bike?

“The median age is 6, but 3 years either way isn't unusual,” says Sheldon Brown, of Harris Cyclery in West Newton, Massachusetts. According to Brown, the best way for a child to learn to ride a bike is to start with an undersized model that allows her to put both feet flat on the ground, so she can experiment with stopping and starting by herself. If you can’t justify buying a bike that will be quickly outgrown, try running along behind, holding your child’s shoulders rather than the bike handles. You want her to get the feel of balancing on her own. Back not up to it? Start with training wheels, but adjust them so they’re a tiny bit above the ground. Lift them higher and higher as your child’s skills improve, until they’re no longer needed.

When are kids ready for their first sleepover?

"Make sure that your child is eager to go and excited about sleeping over,” says Stacey DeBroff, author of Mom Central. “Make sure that you know the parents and feel comfortable with their parenting style. Let your child know that it's okay for her to call you at any hour if she feels uncomfortable, and that you will come and pick her up without being angry or disappointed."

When should we start an allowance?

“Readiness is key for tykes around 3,” says Suzanne Landers Zavatsky, owner of Money Sense Academy in Boston. “Allowances should be used as a vehicle for teaching money, not controlling behavior. In a nutshell, the research says that as a member of the family you should be provided a piece of the family income on a monthly basis, but you are expected to be a contributing member of your family … Extra money making events may be offered, but are not related to the allowance.”