Perhaps I'm stupid, but this whole thread seems to be based on the assumption that the OP cut branches from public land.
Ding-ding-ding! We have a winner! The debris shelter is on my land, and it is not illegal nor unethical nor evil for a family to practice shelter building on their OWN LAND.
What we continue to have here is a failure to communicate.
No assumption about public versus private land changes the debate in any significant way regarding what kids should be taught about cutting live branches of trees. In general, respect for the environment is respect for the environment.
The activity of shelter building can be entirely admirable. The debate is how should kids be taught to do it. I say, no live branches should be cut unless there is a great need, and kids should be taught why.