Actually we are all sexual beings from the moment we are born until the moment we die. Just because a child has not reached sexual maturity doesn't mean they are not sexual, although the experience would be a little different. I even believe there is sometimes a link between an early attraction to diapers and the later sexualization of that experience.
I agree that we are sexual beings from birth. We are born male or female and with a very strong gender idenity (there are of course a few exceptions). Being the father of three I have witnessed very specific gender based behavior from very on in my kids. Also, young males, including babies, often have erections but these are mostly involuntary. No doubt it possible to discover pleasure in our erogenous zones before puberty, but I maintain this is not sexual because it not sexually driven, i.e. no hormones are involved. This why our society refers to pre-adolesence as the age of innoceince.