You have two main decisions to make with Moras: carbon steel or stainless, and rubber handles vs. wood. There are also some very inexpensive low-cost utility knives, under ten bucks, with plastic handles. I like them both, for different reasons. The rubber handles are a bit easier to hang onto, while the wood ones, painted red, have a nice feel and old-school charm.
I prefer the carbon steel for most purposes, but if your boys are young, they will probably be more comfortable with stainless. I started my six-year-old grandson on a carbon Opinel, but soon switched him to stainless for that reason.
If you are buying some for your boys, pick up a couple for yourself, too. If your main purpose for a knife is to cut stuff, it will be hard to do better.