I'm a parent. I think it's sick and disgusting to use children to 'get back' at an ex partner. My bf's ex uses her disabled son to do this and has done so many times over the past few years. She phones/texts saying his is in hospital after having a fit. My bf phones the hospital; they have no record of him being there at all, ever, even in outpatients. She sends tablets with her son when he comes to stay that they have never given him (valium) and she 'forgets' to pack the tablets he does need, to stop him having fits. She tells her son that he has to choose between his mum and dad and makes him so upset (we glean this from the little he can relate to us because of his various disabilities). That is only a brief outline of the things she does, she is truly sick.
She also receives �500 per month 'entertainment money' for her son (it's in benefits, and it is called 'entertainment money'). In all the years my bf was with her and their son, he was never told this, never knew anything about it. He (more than willingly) spent his own money on his son's entertainment and his wife kept that money somewhere, he knows not where, but she never told him about it and she never spent it on her son.
So not only does she use her son to try and hurt her ex - and also put her son's health at risk in the process - but she robs from her son as well. Truly marvellous.