Oh I absolutely agree with you! It's very hard, unless you are a traditional artist, to maintain that innocence in the final look of the piece! And why I find them to be so challenging.
This one shown below is perhaps the only piece I did that I am truly happy with, because of this very subject... But even this, when you compare it to the original stock piece, has managed to detracted from that softness and innocence, which is uniquely a child.
Little Green Apple