See, I would do it like this.
Both salaries are combined. Rent, bills, travel, debt, insurance, childcare, household and daily expenses (everything you have no choice about) is paid (including an agreed amount for basic clothing, basic haircuts, food and fuel, and health - glasses, dentist etc). Savings for DC further education etc, joint savings pots for emergencies, household maintenance or goods replacement and holidays/birthdays/Xmas are put into.
What’s left is split. Half is ‘family fund’ to pay for kids clubs and activities (if not budgeted for already), family days out, birthday meal or takeaways, visiting GPs and so on. 25 percent each is your spending money on personal expenses like additional grooming expenses, clothes, hobbies (and some individual savings would be very wise here.). If this means the family doesn’t have a lot of cash for kids stuff/family stuff, you bias it into the family’s favour, but each adult should still have an equal amount of discretionary spending which is theirs to spend in any way they wish without input from the other, unless they agree it simply isn’t possible in the budget. Everything else is a compromise.
You’re a family, you pool resources and redistribute according to need. And you sit down often (at first) and review it. It’s likely that a person doing more childcare will have more expenses that might count as ‘family’ even though the whole family isn’t present, if they are taking the children to play dates and clubs and so on. It’s possible that grooming or image is more important to some members than others and it may be that it is unfair to take say a haircut out before the split if one of you is having fancy high lights and the other has a dry trim. Or perhaps not, if you have a job where that level of presentation is required. Travel costs might come out of your personal pot if you want first class trains to work or a Porsche and the other drives an old banger. It’s a team budget, and team spending. If you’re not committed to that, well, you’re not a team, are you?
I’d be very, very wary of the split proposed. It deeply disadvantages you. He either doesn’t know or care about the impact on your personal finances and the inequality in the house. It’s not a recipe for a happy blended family.