Without knowing specifics, it might also be the troops don't trust their
own military leadership to back them up, even if they did everything right according to the U.N.Unfortunately, not many UN missions are set up where both/all sides have agreed to stop fighting one another
Lots more shades of grey there than one might think - depending on the ROE, if a child soldier is not threatening or shooting at someone, maaaaaaaaaaaaybe some discretion is possible, but if they're shooting at someone (like a civilian)? Not so much.