If I'm against child AVs, it's nothing to do with AgePlay. It's because for many people, SL is an escape from the mundane, which includes children.
Many of us have kids running around our feet all day and when we go into SL, the last thing we want is more of the same.
Talking to children can be very taxing as they tend to ask lots of question, need lots of explantions and tell you things that you already knew. There is no doubt about it, it is very hard work.
It may be a role play challenge for you, but for many other people it will be seen as an annoyance, especially if you are going to RP to everybody you meet. Most people will not appreciate you talking to them in baby talk, will certainly not appreciate you begging or pretending to be a lost orphan, and many people will just assume you are weird or possibly perverted for wanting to play a child in the first place.
Playing a child is not a great way to win friends and influence people, you are right, lots of people are against child avatars -- no bashing inteneded.