I have paid my share of these types of expenditures to avoid the atomic bomb that would go off if I were to contest ex. It keeps the peace and to date the expenses have been reasonable.

But most importantly, there are good chances that without my contribution my ex would not sign up for these types of things at all, and then the kids would suffer.

Agreed and doing the same. No contribution from the other side. And as you said, if I stop, the child would suffer...