What makes you want to have 4,5 or more children? Presumably you are well off so you can afford big houses with each child having their own room, 7 seater car, huge food bills etc.
I have had 4 kids in just over 7 years (first when I was 23 and final at 30 in 2019)... and, at the risk of sounding like a knobhead, the honest answer is I am just very good at it. Practically in terms of falling pregnant easily, having easy pregnancies - never sick, simple vaginally deliveries, pain free breastfeeding until aged 2 each time - so nothing to put me off or make me think twice about my own health, etc. We are not rich but met very young, getting on the housing ladder in 2007 when a 3 bed semi was £90k in our area; we have gradually upgraded with small windfalls and with home improvements and it has taken 3 or 4 houses moves to get where we are. We have plenty of space - our house is technically a 7 bed but we only use 5 as bedrooms.
We both don't really have careers - as in our jobs arent a calling or a vocation but just something to do until our tea is ready - but we are reasonably well-paid (not by MN standards! £65k a year between us) and quite easy jobs so are quite time rich. We really wanted 4 kids and really enjoy having them. We have one set of local grandparents, fairly local, but they don't do loads of childcare, just a school run and teatime a week - at its peak they did one 6 hour day a week which we were grateful for but didn't need. But crucially I (especially important as the primary carer imo) am well supported emotionally by lots of friends I have known since childhood, and we as.a couple just really like each other and get on well.
Our life is busy and fun and yes, expensive, but it is not especially hard work. The things that have been tricky - death, redundancy, illness - are tricky with one kid or ten, and our four wonderful kids are a.comfort and a joy (and yes, a worry, but a powerful and purposeful worry if that makes sense. When things are bad we keep going and make changes for them.)
It is totally different strokes for different folks and in the same way I look at people with hard jobs (as an example, doctors) and think "What on earth do you get out of doing that?", I know my life choices are baffling to just as many.