Raising kids is a FT job, and a career is a FT job. So at the least you need to involve childcare, as you already know.
But typically childcare is limited. Especially now, if your child is sick, or has an accident, or there is a problem, someone has to be there to manage it. If your childcare provider is ill, same problem. Someone still has to manage the care or school stuff like homework or projects etc. All this even more so if you find you have a child with special needs or some other extra demands.
I think this is the real reason one person's career often has to be less demanding, there just has to be some level of flexibility and availability.
In families I know where both parents work at demanding careers, they usually need some extra help, beyond just standard childcare. Usually a nanny, even if only part time. Often someone comes in to do some cleaning as well, maybe weekly or biweekly.
Even people in careers where they both just work a fairly standard 9 to 5 pus commute, who can't afford a nanny or maid, often seem to struggle with it and many burn out and find they need to make some adjustments, at least until their kids are over about 10.