Reddit reviews Camp Out!: The Ultimate Kids' Guide

Ohhh! That sounds like such fun! I went through the same phase as a 7-9yo girl w/ a hovering mother. Went off into the woods behind my house with my cousin for a long weekend every year.

Scavenger hunt sounds fantastic! You could even get her a compass and a "map"(one you made of your back yard) for her to mark off what she found. One thing I would do, is have them involved in the things you have to do for safety, i.e. gather wood and set up the fire for you to light. Hey, and good job supporting your niece's interest in this. This is what fond childhood memories are made of.

Here are some books you might want to look at for your niece so she can "study" before her adventure: Camp Out!: The Ultimate Kids' Guide

This one is for a kids a little older Ultimate Explorer Guide for Kids

How well are their reading skills? This has been a life-saver for a while: https://www.amazon.com/Camp-Out-Ultimate-Kids-Guide/dp/0761141227/ref=sr_1_5?s=books&ie=UTF8&qid=1538072538&sr=1-5&keywords=camping+for+kids

For two boys, they can feed off each other and try things in the book. Just be careful when they get really quiet.

Also, camp/park closer to the bathrooms than you normally would. Wait, you have boys though....nevermind.