Some small children make up their own languages and ways of communicating. Then, one day, they start chattering away and you can't shut them up!
Every kid develops at his/her own rate. My Mark didn't walk, until he was 16 mos old. Some people made comments and I told them that he'd walk, when he got darned good and ready. Sure enough, I woke up one morning to find him ambling around my bedroom, emptying the dresser drawers.
You spend your kids' first two years, teaching them to walk and talk and the next 16 years, telling them to "sit down and shut up".
Raising kids, the best thing is usually to trust your instincts. Kids just will NOT be pigeonholed. Despite the efforts of so-called "experts", most kids develop at their own speeds and darned if most of them don't turn out, just fine!
Hang in there. At 3 1/2, all that a kid really needs to know is that someone loves them , how to play and don't pull the kitty's tail.