They're sold as a tool for enhancing the security of your children, but it's fairly trivial to subvert them to both not do the job they're sold for, as well as

They're sold as a tool for enhancing the security of your children, but it's fairly trivial to subvert them to both not do the job they're sold for, as well as giving the attacker extra information they could otherwise have only got through proximity. If there's a real risk (and while it might be relatively rare, real risks do exist) then the regular routine is hopefully already set up to mitigate the risk. The value to the attacker is in being able to take advantage of deviations from routine that would apart from the watch be invisible to them.