Was it? Scott was a child soldier, and trained alongside the rest of the O5 to get involved in stuff that no kid his age should have. That was almost always the case but something that was made a big deal until Schism.
Considering he went along with it, had no regrets and didnt call out Xavier for that, his stance wasnt really OOC. It made even more sense given the deciMation. The children needed to know how to defend themselves. Mutants were nearly wiped out and groups were still out there trying to slaughter what few remained. The adults arent always going to be around to protect them so they needed to be equipped with the tools and sense to do so themselves. Its not practical to expect them to just stay in the classroom with no life experience when the world wasnt stopping for them to catch up. Cyclops was right