I think that if after 3 your child doesn't start speaking at least some sentences, then probably he is having a speech problem but nothing that the science and the speech therapist cannot solve.
Speech problems are very common in toddlers and has NOTHING to do with the intelligence of the kid himself.
Put the example of Einstein who started speaking at age 4...and look the genius he was! (wondering now if his talent in the mathematics was like a 'clue' of his speech problem, after all, they said that who likes 'numbers' don't like words too much
A visit with a peditriatian and speech therapist will be able to help a lot.
My kid doesn't talk and he's two. I guess he supposes he doesn't need to because he uses other methods of communicating. When he's thirsty he will grab his cup and put it into my hand. Also he is so physically active and doesn't have the attention span to pay attention to me trying to teach him words. He is more apt to copy another child's speech. After coming home from a friends house with a child who speaks, my son came home saying a new word each time we were there. He didn't keep using it but he learned a new word and used it for a few days. I think the influence that children have on other children is very important.
I also think differnt kids develop at different ages, different factors also influence the rate at which a child starts to speek. For example if a child has other siblings in the house he will hear them talk and also interact more with them this child will learn to talk more compaird to a child who hardly gets to socialize, socializing is also important for young children!
also when a baby is in its first few months the mother should still talk to him/her because the words may get into the childs unconcious mind...children also learn words from TV but its still better to learn from a person infront of them as tehy also get to co-oporate and be social, repeating words is also a good way for tehm to learn new words, when you are feeding your child food for example talk to it and tell it what you are making for lunch today ask the child what food it likes ovcorse if it cant talk it wount answer but you will still be teaching it and show it the food and say the names of what foods get it to repeat the names of the foods as you put them in there mouths, children enjoy learning thru playing!
I know that with my oldest daughter (who is 6 now), by the time she turned 2, she was already speaking many words and short sentences. But with my youngest one (she is almost 2) and she is speaking very little words and maybe 2 word sentences. I do speak slowly and clearly to my baby all the time. That way, she will learn more words.
I'm seriously thinking in taking my 3 years old to a speech therapist or a child psychologist. He is supposed to be speaking by now, but he only says properly very few words, the rest is baby talk. He's also a bit more immature than the kids of his age (he behaves more like a 2 years old) that's why I was thinking in taking him to a child psychologist. I'm a bit concerned about him.