My daughter and I ride a tandem, and she really finds her toeclips beneficial (without straps, a.k.a. half clips) as they stop her feet bouncing off the pedals over bumps or sliding forwards.
However we've already broken one (just cheap plastic but a very good fit) because it hits the road when I'm riding solo to pick her up. A smooth road in a straight line is OK, but pedalling through corners (e.g. from a junction) or even an extra steep camber means pedal strike.
Riding solo I can strap the toeclips to the cranks, though even this isn't perfect - the front can still hit the ground and that's what finished one off. But I have to remember.
To make it harder she sometimes rests with her feet on the toptube while I pedal, putting her feet back in while I freewheel, so I'd like a solution that works there too.
We've discussed SPDs but she's not keen, and given the rate her feet are growing neither am I.
So what other solutions are there for mild foot retention that don't get damaged by pedal strike when not in use?