I hate to say this, but when going out with kids, it really has to be the kids' trip, not yours. Being prepared for rain is part of this. A dining tarp is a big help, even though it adds to the weight. So is adequate rain gear for the kids and a change (or even two) of dry clothing, at least for bedtime. So are games that can be played under the dining tarp or in the tent. Most kids love splashing through puddles and getting muddy; it's part of childhood! The parent's job is to make it fun! Insisting that the kids conform to your idea of a "good trip" is liable to turn them off backpacking for life.

From an experiened parent of four and grandma of six!