I'm suprised noone's replied to this
Are your trails groomed? Because longer track sleds aren't very good for groomed trails. I don't know polaris but i believe the RMK trail ahs a 136" track which would be better for crossing over from trail to powder. If you're looking into buying a newer sled, look into the; Polaris Switchback, Ski-doo MXZ Renegade, or Arctic cat Cross Fire. These sleds are designed for trail/powder riding. I would suggest going to your local dealers and looking at the sleds, sitting on them and asking lots of questions. You'll start to get a feeling about which one you like the best. Another thing is that in powder a lot of steering and control has to do with the weight transfer of your body, so it may be hard to play around in powder with one of your kids on the back. Reverse is also a very nice feature to have, i think you can get reverse on all the brands, but ski-doo makes electronic reverse standard on all their sleds. It add's no weight and doesn't cost anything.
If it comes down to the two sleds, than i would go with the RMK Trail if you're riding groomed trails a lot but venturing off into powder too, but if you're riding powder trails and powder everything else than go for the summit.