If you want them to love the outdoors and make it a part of their life forever get a tent. Make it comfortable. Make the trip easy and fun.
Light weight means nothing if everybody hates it.
Back when I started with my kids I carried a 110 L pack to play Sherpa, but they loved it. I slowly added more to their packs and less to mine. Now I just did a trip on the SHT last week with an Exos 58. (See pic below.)
For 4 people the lightest you are going to find in a double-wall is the Hogback that I know of. That is what we took on that trip. Hmm, can I do two pics?