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
These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.