We do this all the time with our kids. eg Halloween: you can eat <large percentage> your sweets now but we will eat the rest when you've gone to bed, or you can

We do this all the time with our kids. eg Halloween: you can eat <large percentage> your sweets now but we will eat the rest when you've gone to bed, or you can have <smaller percentage> now but have some left for tomorrow and the rest of the week. Our eldest (he's 4 now but we've been doing it for a couple of years) responds really well to that. In fact a 100% pass rate so far. Which is unusual for a boy of that age from what I've read.