You may be concerned if your preschooler starts to stutter and stammer a lot. Don't worry about it. Stuttering and stammering are common at this age due to the lag between a three-year-old's ability to think and his ability to form words. Especially when he's excited or upset, your child's ideas will probably out race his vocabulary.
In some ways, despite your child's improving vocabulary and language skills, language actually becomes more difficult at three. For one thing, your child now knows that there's a right word for everything, and he wants to use the right word all the time. For another, he can now talk about things that he's not observing directly; about ideas. This move toward greater and greater abstraction is also a challenge.
You can help your stammering child by listening carefully and patiently and trying your best to understand what he is trying to say. Try not to become impatient and finish sentences for him. You can also help your child feel more relaxed in conversation by showing him that you enjoy talking—and listening—to him. When your child is talking—and especially when he's struggling to get a word out—pay attention and try not to wander away (literally or figuratively). Give your child time. He will almost definitely grow out of his stammering and stuttering.
Another problem many three-year-olds have is mispronunciation. Again, don't worry about it. Don't make a point of correcting it, because this may make your child more selfconscious about speaking and worsen the tendency to stutter and stammer. Instead, merely pronounce the word the right way when you speak it and give your child the opportunity to correct himself. Like good wine, your child's pronunciation will improve with age.
Your preschooler may at some point revert to baby talk (or continue using it long after outgrowing the need to use it). If you have always indulged your child's baby talk, he may think that adults find it cute.
But if you want your preschooler to stop using baby language now, try to avoid doing an immediate about face. Don't suddenly refuse to acknowledge your child when he speaks in baby talk. Instead, if you answer your child's baby talk with baby talk of your own, first resolve to stop speaking any more baby talk yourself. Then, in responding to your preschooler, translate everything he says in baby talk into grown-up talk. Within a few months or so, he'll no doubt stop using baby talk entirely on his own.