Seriously. Kids awake 12 hours/day when they're young, overlapping with work during the week which makes that calculation easy. 12x7 = 84. You can kind of do other productive stuff during that time, but not much. 8hrs/night sleep is 56 hours/week, assuming you don't need some time to wind down for sleep (most do).

84+56 = 140. 168 hours in a week. That's 28 hours left for everything that's not kids, work, and sleep. Fixing stuff around the house, keeping your relationship with your partner healthy-ish, prepping for the next day so you aren't constantly running late to everything, cleaning, entertainment, learning, everything. In practice you'll have an average of 2hrs/day that's actually free, maybe, without neglecting sleep, and they'll be your worst, lowest-energy, lowest-motivation hours (work gets all of the best hours 5 days/week, kids do the other 2 days)

Maybe don't have children unless you can afford it? I've put off having children until I have the financial resources to raise them. What is stopping others from doing the same?