Any system which relies on preventing kids form exploring while outdoors seems to be both self-defeating and unlikely to work.
My advice is to talk to them about what they should do if they do get lost so they can help in their own rescue. Similarity putting too strong a prohibition on wandering off is only likely to make them more prone to panic and forget safety instructions if they do.
Simple things can make the campsite easier for anybody to find if they do get lost at night.
- set up a perimeter line with high visibility (even glow in the dark cord) this gives a bigger target to find in the dark
- Put out a safe light overnight in a visible spot, a chemical or solar powered lantern is ideal
- have an agreed system for signalling, for example if you notice somebody is missing blow a whistle 3 times every minute and set up extra lights ideally a strobe.
- Ideally 'home' lights should be coloured eg blue or green to make them more obvious and avoid any confusion with lights from roads towns etc.
- Give everybody a whistle and key-chain light on a string if you put it in a bracelet then kids are more likely to keep it on.
It is also a good idea to conduct a 'lost' drill early in the trip, it should be easy enough to make this a game. For anybody getting lost the biggest danger is panic so going through the emergency procedure in a fun way will greatly improve their confidence.
Teach kids that if they realise they are lost they should stay put and shout out.
I would also endorse the 'buddy' system from a previous answer, pair kids off and encourage them to look out for each other, emphasise that if they are worried about their buddy they should ask an adult for help.
My own feeling is that giving kids a bit of agency in looking after themselves and each other is by far the best way both for them to get the most out of the experience and keep them safe.