Is my preschooler behind because she's not reading yet?
Not at all. Kids typically start learning to read in kindergarten. And, although you may hear another parent boasting about his or her preschooler's uncanny reading ability (or be tempted by those "teach your baby to read" programs), the average age of reading proficiency is 7.
So, unless your pre-kindergartners are showing an active interest in learning to read, your time is better spent reading with and talking to them and helping them develop the essential social skills (cooperating, sharing, making friends) that will help them thrive in school. Check out these ideas for helping your child build oral language skills.