Most of these posts are about having young children.
I have 4DC, and I manage to;
Go to the loo alone
'Nip/pop' somewhere quickly
Have lie ins
Go out with my partner.
My DC range from 17yrs - 7yrs. So things change as they get older.
Having children does change your life - in the early days it's the practical things, such as bigger car, house, loads of stuff to cart around, no sleep/time etc, but as they get older, they get more expensive. Think, school residential trips, sports activities, instrument lessons, holidays are more expensive, clothes/shoes are more expensive, then there is; 6th form transport costs (currently £1,000 a year for 1DC) driving lessons, car insurance, university top ups, etc.
As they get older, it's the responsibility for ensuring they are good people, it's the coaching, mentoring, teaching ethics, life skills, budgeting, cooking etc, treating people with respect, being inclusive, tolerant etc. Being responsible for how an adult turns out is way more of a life change for me, than getting no lie ins for a few years.
You need to think through the whole thing, OP, you're a parent for life, not just while they're toddlers.