stuttering
When my son was about that age (he is 18 now), he stuttered. He could not get the word out that he wanted. I asked the speech pathologist at the school where I was and he said that kids' thoughts are way faster than their speech ability as toddlers. I let it go and did not make any mention of it to my son and eventually he grew out of it. If the stuttering had continued, I would have sought help. But he has been fine ever since.