We have a formula for deciding the cost of children’s basic needs: the national foster care allowance. That should be the minimum for every child, split in half between parents.
benefits for children would go to both parents on a 50/50 basis so a non resident parent on benefits would no longer be paying a paltry £5 a week.
The penalties for not paying maintenance would be high
If you want to encourage parents to physically step up for their children you mandate an additional payment for parents who do less than X percent childcare.
At the same time it also makes all families consider the impact of another child in a new relationship as maintenance doesn’t drop.
Increases tax receipts as no motivation to hide income if for example self employed
The downside is families where the other parent is genuinely able to avoid paying eg dead, are not known eg donor conceptions, move abroad and there would have to be benefit adjustments for these families to ensure children had sufficient money as these parents were paying alone.
The biggest downside for the government is that benefits would also genuinely have to meet children’s needs. On the other hand it would tackle child poverty most effectively and highlight how many families raise children on insufficient income for their needs.