The mutants recruited to the House of M are similar to the New Mutants living at the Xavier Institute. These mutants, however, either have a taste for fighting authority, have had horrible experiences with humans, or are just vulnerable enough for the Brotherhood to twist them towards there cause of Mutant Supremacy.
While selecting younger mutants from the same stock as the X-Men are, the Brotherhood is subtle and crafty, taking care to avoid detection by the X-Men. For this reason, the majority of their recruits tend to be slightly older, having already lived in fear of humans long enough that they are more open to the Brotherhood's plans for the future.
That said, the majority of the Upstarts do not even know of the existence of the Brotherhood or their plans. The staff at the boarding house, while mutants, take care to not reveal their true intentions.