The three children of my youngest daughter and her husband have always been very affectionate. Hugs and kisses when we all visit each other...the same when it's time to say "see you soon!". The youngest are identical twin boys. Such look-alikes that many in our family could not tell them apart.
Anyway, when these little guys, at ages 3, 4 and maybe 5, gave hugs and kisses, many's the time they landed on my backside. What did they know or care? You can imagine the laughs we had over that.
The perversion in this little boy's case lies with the accusers, IMO.
My young cousins were the same way. They are getting older now, so they don’t hug much anymore. I know what you mean.
It is possible that children can be exposed to sex at a young age depending on their home life, but I didn’t get the feeling from this little boy based on his father. This sounds innocent, and the aide completely overreacted. If I were the father, I would find another school for my child. I wouldn’t send him back there.