Holding a child back because her motor skills/processing speed haven't caught up to her other abilities is like...
Not feeding a child the main course because they won't each their spinach.
- I think this conveys:
1. the thing they want to do is good for them too, as well as attractive to them
2. While the thing they don't want to do is good for them
it is a taste for that comes with time. You don't stop trying to feed them the spinach from time to time, you just don't make it the only thing on the plate
3. I think also 'feeding' the brain is just a good basic analogy, as is the inverse of 'starving' it.
