hierarchy start order

How can I ensure a children will be awaken or started after their parents?

You can’t rely on Unity for this. but you can make your own functionality to ensure call order. Especially easy if it’s always the parent that has to init it’s children. Use the Awake/Start in the parent and use a Init in the children that is called by the parent.

[Edit]Reading what’s new in 3.4 it says you can, here Edit->Project Settings->Script Execution Order.