Just found this about the rip off known as Jamster. It's a bit of a long read, but there is a bit quoting Austrian law, which has a equal liability here for recovering your money
"..........Additionally use the following strong argument:
I declare that my underage child is contractually not capable (or contractually capable only in a lower degree) and that I do explicitely not consent to the contract that was concluded by my child with Jamster-Ilove.
Legal Transactions of minors are legally ineffective without the consent of the parents, according to the famous german expert for criminal law Udo Vetter (
www.vetter-mertens.de/ and
www.lawblog.de). Jamster-Ilove-Orders done by minors are as long legally ineffective until the parents have agreed to them."
If your kids are under 16, they are minors by our law and cannot enter a contract, therefore the contract is void.