One tip: instead of making a borax solution in hot water which can irritate the skin of some, use a contact-lens solution that has a borate-type preservative it in it. It might cost a little more, but it's a lot safer on skin and easier to handle (comes in it's own bottle with a cap).
Borax has been getting negative press recently and I see people recommending contact lens solution as an alternative. But why is contact lens solution safer than Borax, when the active ingredient in both is boric acid?
I believe it's safer because when people make their own boric acid solutions using Borax 20 Mule Team powder and water, they make it way way too strong. Handling the raw powder isn't a great idea for kids either.
Using the contact solution still gives the necessary catalyst, but kids can handle it safely. It may take a bit more volume to make it the reaction happen, but it still happens.