By the age of three children are usually able to identify boy and girl toys and know which toys are supposed to be theirs. Whether this has anything to do with gender identity is another question though since this behavior can also easily be explained by mob mentality and social conditioning that influence the young brain to give the answers that it thinks people want to hear. There is a good chance that many children sexual identities are shaped by the influence of those people around them and how they treat gender. for example young boys in many families are scolded for playing with dolls, if this case the child never really has a chance to form his own gender identity, because one is forced onto him by his environment. For many people this leads to a a questioning of ones own sexual identity later in life after realizing they have been living the life they were told to live and not the one that they actually related to.
