My kittens just turned 5 mo old. Last week, they both had their adult canine teeth side by side to their baby teeth on the top only. The adult teeth almost got as long as the baby teeth until the baby teeth fell out. I can't say if this also happened on the bottom canines since those were lost about a month ago while I was out of town.
Usually they do still come out but occasionally the baby teeth will not fall out on their own.. so just keep an eye on them, and let the vet know whenever your next visit is if they don't come out. One of our dogs has two baby canines that never came out, and need to be pulled when he gets neutered, since they already are gathering tartar while the rest of his teeth are pearly white.