Why a child?
Personally it just makes it easier to make a chaotic and playful gameplay that feels authentic. I also like the layer it adds of the player in a sense being responsible to take care of lily.
The games premise is a lot like taking care of a child. Even though you’re caught of guard and sometimes don’t understand what is happening right away, there is always a very logical reason to why. Just with a child, often a simple answer doesn’t exist, but with compromises both Lily and you, will enjoy your time together.