This is a fascinating subject - and particularly since Aelia mentioned animal intelligence, which is of real interest to me personally.
I honestly don't know anything about brain development in children, thank you Mouse for posting that link - not light reading, but very interesting if you take the time to read it with a big medical glossary to hand
But as usual with me, it is the animal intelligence sentence at the end of Aelia's first post that piques my interest, so I'll comment on that and hopefully it won't be too off topic!
Firstly, a link:
http://www.alexfoundation.org/
to current ongoing research into parrot intelligence (I'm sorry, I just know more about parrots than other animals, I know I'm a parrot bore) - this is a serious research project run by Dr Irene Pepperberg which has been going on for years, and has demonstrated that parrots don't just mimic when they learn to talk, but have complex mental processes - they have the cognitive abilities of a 3-4 year old child, putting them on a par with the great apes! This is in part explained by the fact that parrots are zygodactylous - they have 2 front toes and 2 back toes on each foot, meaning they are very dextrous and can manipulate objects, use tools etc, and are very long lived.
I'm not going to overstate it - this is basic intelligence, a parrot is never going to build a space shuttle or design a bridge. To paraphrase Pepperberg, a parrot won't ever tell you what it did yesterday, or what it expects from tomorrow - complex abstract thought is not the way their brain works. They can work out quite complex things in the here and now though, and will be innovative in tool use, trying out different things and learning from their successes and failures.
My baby Senegal parrot for example worked out with alarming speed how to open the door of his cage. He has a motivation to do this, obviously it is more fun to sit on me and cause havoc around the house! He would watch very carefully whenever I opened the door to let him out - although I don't know what was going through his head, I could see by his eye rings and head posture that he was focusing intently on my hand. After watching a few times, he started to try by himself, using his beak to squeeze pairs of bars together until he found the right pair - so motivation, observation, reasoning, and a little luck were involved. Then I put a screw-link on his door to keep it closed. Again he watched carefully, and now can undo the link halfway. (I have had this bird for 6 weeks). None of this is that astounding, but the roof of the cage also opens up - with a similar catch to the door. This baby parrot has made a logical connection, and
even though I have NEVER opened the roof of his cage he is now working on opening the latches there too, using the same method as he used on the door.
There are some things which are beyond animal intelligence. Chimpanzees can be shown how to knap flint to get a basic sharp edge. If they are given flint, they can do this once shown. If they are given a flint knife, and a box with food inside, they will use the sharp edge to break open the box. However, give a chimp a piece of flint and a box of food, and it will not be able to make the connection between them - the knife goes unmade, and the food uneaten.
Another interesting piece of research which involved chimps - a trained chimp which was used to being given commands in English and showed understanding of many phrases, was shown two plates of food and told to choose one for himself. Instinctively, the chimp reaches for the bigger plate. When told to choose a plate of food to give to another chimp, the chimp again chooses the biggest plate, it is as if instinct won't allow him to choose the smaller plate, even if he will get more food as a result. The same chimp was taught basic counting, and could understand that 3 was greater than 2, 4 greater than 3 etc. - when the experiment was repeated using numbers to represent bananas instead of the physical presence of the plate of food, the chimp was able to select the smaller number of bananas for his companion so that he got more bananas - it was the presence of the food itself which caused instinct to override understanding.
Very interesting, sorry for the long post!