I live in Missouri and my ex is currently $2000 behind in child support. Will child support enforcement automatically intercept taxes or do I have to request this be done? I have never received state assistance.

This is REALLY a legal question, but I will answer it to the best of my knowledge.

Virtually all garnishments of tax refunds are initiated by the state agencies which enforce child support court order.

So, if you have NOT involved the state courts or state agencies in the collection of your child support, then it is likely that there is NO garnishment order in effect with either the IRS or the state tax department.