Get a huge pack. If weight is the only difference, why not have more space than less? Especially with kids. If you get a small pack, you will just end up with a bunch of stuff strapped to the outside. Ji. I have a Kelty White Cloud. 7,000 inches, modular, strips down to 28
ounces in the lightest mode. Works in the winter for the big sleeping bag and cold weather ggear too. Jim
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These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.