Involving parents is vital. One of the best things about scouting (from a parental perspective) is that my son and I have had more focus for our fun together. Our pack is great about giving parents the opportunity to be involved.
One thing that can help is to have new parents leaf through the manual for a few minutes and pick one achievement they feel they are really well-suited to helping the kids with. You might find someone who is a chef, a carpenter, a thespian, a police officer, or an artist. Whatever! There's going to be something that person can look at and say "sure, I can help with this one." Then, get them to pick a night when they will want to work on it. It might be several nights. But if each parent is already committed from the start to helping the boys learn to do something, then each parent is going to feel more committed to showing up.
For example, there's fellow in this town who can cook almost anything you can name in a dutch oven over a campfire. Amazing guy. Give him a job of teaching kids to cook that way and he'll probably have them make a pineapple upside-down cake, a main dish, and some sides. The cake is the real show-stopper. Have the kids show up early and tell everyone the boys are going to make supper tonight, perhaps assign everyone certain ingredients to bring for it. Kids learn loads, there is at least one thing to check off in the book, the parent who led that night feels a sense of ownership in the den, and the kids can't wait to see what they do next time.
I'll be leading a den full of Bears next week with getting their Whittling Chip cards. As a wood carver (hobby level), I am very attached to this particular craft and want to encourage it among boys. My daughter will be present as well because I want her to learn it, too. I'm giving up my usual Tuesday plans (my wife normally takes our boy to CS) so I can do this. You bet I feel attached to the den!
Anyway, while it is totally vital that kids have fun, I think making the parents feel accountable to the whole den is a part of ensuring the kids will be there. Sort of the long way around to making a short point.