I have one of the multi angle edge/base guides and they are very functional, adjusted gently not an issue, inexpensive and a good start to learn tuning without a painful expense.
Yes, there are better specific tools, but truly it's in the hands of the user that gets the result, learn simple, master it, upgrade to perfect it as and when needed.
Your kids are better of learning how files and stones cut to leave little or no burr, this alone will serve them better in the long run. Look for threads "my ski after a tune....sucks" to get an idea of how many still don't grasp this concept (including shops).
Keep the expense down, go slow and easy, practice and make it fun. They might like it and become the best tuners out there.