St mary's is a high alpine lake , so wind is always a factor. I would not suggest takeing your son out if the wind is to crazy. You should also check the rules and regs before, I dont know if they allow watercraft. As always have fun fishing! -Tightlines!!!!!!!!!!
You'd be hard pressed to get a boat up to the the lake, Its a steep 1/3 mile hike up. I see people who "Think" they can pull a sled up in the winter, lets just say most people fail. Don't waist your time, just hike up and fish kastmasters, chuck em way out, and you'll get the brookies.