suggestions for using my iPhone 6 and Watch 3 to track my kid at Disneyland?

My family is going to Disneyland, CA Adventure and Legoland in a few weeks.

I have an 8-year-old son who is fairly mature and independent, but I want to have a way to help track him if he gets lost.

At the park yesterday, he took my Watch 3 (+Cellular) and was having fun calling my wife from the playground where he and his friend were, and it got me thinking...

Can I use the combination of her iPhone, my iPhone, and the Watch to help track the boy if he gets lost at the theme parks?
Obviously he can call my wife's phone from the Watch (but can't call my phone since they're linked).

Is there an app we can use to track his whereabouts if he's wearing the Watch?

I'm avoiding getting him his own mobile device until the last possible minute....