The MacLaren is the official tartan of the scouts, they don't have an official kilt. And most of the gray hairs in the BSA take issue with kilts being worn, most of the time stating its not official uniform. Luckily, attitudes are changing.
So for the Cub Scouts, I have never seen a pack that had the cub scouts get anything other than the shirt, hat, and neckerchief. Usually the most common bottoms worn is jeans. So that certainly leaves it to: uniform bottom wasn't chosen, we opted for a kilt. Doubtful that the den leader will have any complaints, but you never know about the Cubmaster. The Cubmaster is the one that has to deal with any parents that might complain, he is also the one who will have to deal with any complaints from the district or council.
Back to the MacLaren, it is the official scout tartan, as a scouter you are fully capable of wearing a MacLaren kilt, but you are not limited to it. If you have clan affiliation then by all means wear your clan tartan. If you complete Wood Badge you can join the Clan MacLaren Society of North America as a Wood Badge member. I'm sure there is a ton more scouting related things I can talk about but I'll leave it there for now.