“ but as soon as something changes eg you move house, whoosh, away goes child no.3s money.”
Thankfully that is not true , you will lost transional protection for other reasons of yiu hsve a new partner , stop working etc ( not move house) but you won’t lose the extra money for a third child.
I moved house and it was treated as a change in circumstance. One of the problems is you get a different answer to a question every time you phone them. It also depends who processes your claim. You rely on them to implement the rules correctly, but they aren't familiar with them. Even CAB have to look it up as its all different. By contrast, at the Housing benefit office there was always someone with expertise based on knowledge of a system they'd been working with for years.
With regards to children, I see they've brought in new legislation, but it only counts for children born before 6 April 2017 ie babies not exempt.
*Quarksand Leptons
I know it’s a vast and complicated question but as someone with direct experience of it, what do you think we can do to make the system fair to women and children? *
This is difficult, but surely giving half to each parent by default would make sense. My ex changed the arrangement so all the CTC got paid into his account though. There is not a lot you can do if they're determined. He used to demand my payslips and get me to write a cheque to him as well. He worked out my allowance for the month and left that.
Financial abuse from my middle class privately educated ex was not well understood by professionals I encountered including social workers and barristers. The police are definitely our greatest advocates for this apart from, obviously, actual women's groups and domestic violence charities.