As a kid, my mother chose the toys we would receive during our birthdays and during Christmas. The toys she chose emphasized the confluence of simplicity, versatility and complexity (kids aren't stupid, ya know): Blocks, Erector sets, games such as Monopoly & 'Happiness'.
I would be puzzled at first of her choices and only later would I discover its long term play value (heck... the concepts of the game 'Happiness' still intrudes upon my thoughts today).
One year, Dad did the choosing and he went to us one by one and asked us what we would like. When came time for opening the presents, I was over joyed that I received exactly what I asked for: It was only later that I realized that something was missing with these toys and stopped playing with them soon afterwards.
Nope... not easy choosing toys. Santa must be wise, indeed... :)
"..confluence of simplicity, versatility and complexity..."
A good example of Simplicity and Complexity is the game of Chess.
Sorry for being ambiguous.