As with any RPG game the only thing that matters is that everyone is having fun. I play with myself in D&D 5E for the Rise of the Dragons stuff (started playing games with 4E but that was too slow, and Pathfinder was confusing to me at the time with spells). As a DM, and players, if I do not like something I change it (ex. loot rolls sucked, so I rolled again and got something interesting).
You do not have to make things too easy or too hard. I personally enjoy a little difficulty, but love loot and rewards. If your children like magic items, then shower them in cool stuff. If they like to slaughter through a dungeon easily, focus more on story to keep it interesting. You can always change encounters or traps to make things more difficult for their level (and gear). That is the beauty of DMing, you create everything!
I DM for family a few times with 1-2 people. I enjoy their creativity, and they enjoy the surprises that happen just as much as if combat is easy or difficult. Use the books as guidelines and modify it as you see fit. As it roughly says in the 5th Edition DM Guide "If you think a level 1 character possessing a Ring of Invisibility will be the start of an exciting campaign, then go for it!"