the answer isn't straight forward. You would have two options.

Option 1: both your children don't count all year. you only take on 3 kids. Only taking on one child under 2 as your baby counts as the other under 2.

Option 2: Your 4 yr old doesn't count during school months (must be in a government funded school full time) so between sept - june you can have 4 dc kids. BUT you can NOT take on any child under 2 as you will only be allowed one under two and your baby takes that spot. And during july and august you would have to get rid of one dc child as your 4 yr will count for those two months.

By the time your baby is 2, your 4 yr will be six and not counting in your numbers at all. Can make it work with only 3 kids until then?