SEA is busy during cruise seasons and often has ATC delays - either from a departure or arrival aspect (or both) so the dates of your trip can make a difference. Also, right now the train to C is down (being remodeled) so you will need to walk. Your SEA BOI flight could depart from C2x gates which is somewhat close to those arriving from N gates, or it could depart from C10x gates which is halfway down the terminal, or it could depart from C16x gates which is at the very end of the terminal - a long haul with little kids. The train is supposed to re-open in late 2019 which would make a connection between N and the end of C very quick but I would ensure all the kiddies went potty on your arriving to SEA plane before landing. The flight to BOI may be a Q400 (which always boards much later than stated) and that "may" allow more than enough time (kiddie potty runs at SEA) for your connection. Bottom line is that you will be stressed. You might want to consider spending the night in SEA - book a later flight to BOI so that you can take the kids on the light rail and maybe do Flight over Seattle or the Ferris wheel.