My advice would be to zoom out and look at the bigger picture. First decide what you (as a family) want to accomplish, and why, and then figure out how. Then do the same on a lower level to determine the rules.
What: We want the members of our family to be safe.
Why: Because we love each other and don't want any harm to come to us.
How: Therefore, we will need some rules to guard our safety.
What: We want to know where you are and where you're going to.
Why: So we know where to reach you in case of an emergency, or where to look if something happens to you.
How: Therefore, let us know where you're going, don't go somewhere else without letting us know, and take the emergency cellphone (assuming they're too young for their own cellphone) if needed (for instance, when trick-or-treating).
Of course, you could make 'communication' the goal and arrive at a similar rule, but from a different viewpoint ('so we know where to reach you if plans change / when diner is ready').
The point is that rules by themselves can seem arbitrary and be subject to rules-lawyering, while this way, they're part of a bigger whole. (For instance, 'safety' can lead to not just rules but measures as well, like smoke detectors and fire blankets).
While the parents will have final say, the children can be involved in setting up the rules. That way, they should feel they co-own the rules; if they break a rule, they not just broke your rule, they broke their own rule.
Also, don't be afraid to accept rules the children may come up with. The goal 'hapiness' can lead to a rule that 'the family should play a game for at least an hour each saturday'.