Now I think about it, we started when she was about 2, leaving a marmite rice cake in a bowl outside her door, with a bottle of water (with a sports cap), that was just enough to delay her slightly.
As she got older, I'd put some greek yoghurt in a bowl with cling film over the top in the fridge, and a plastic cup of water with tin foil over the top and cutlery on the table.
Now I just say "no cartoons before 7", and she sorts her own water out, makes some bread and butter (don't trust her with the toaster yet) and helps herself to yoghurt.
She woke me up at 9 this morning, happy with that!