tbh i think that families really must make a solid plan for childcare before one or both of the parents take on an outside job.
At the end of the day, we are offering our services to an employer and they need to be able to rely on us. Obvs there are difficulties that might arise for anyone, parent or not, but with children there are what we might call the known unknowns: chicken pox, D&V, headlice etc etc. You can't know when these things will crop up, but the probability is that they will.
In my case, i live far far away from all my family and 2 weeks before DC1 was born we moved to a new place. No network. So for the first 3 years i was the SAHM even though we could barely afford it.
After that - we moved again shortly after DC2 - i got a job and DH was the SAHP. After that we both worked and paid out a shedload of cash for a childminder/nanny. We made sure to get one who would cover sudden unexpected illnesses etc, and even then it was bloody difficult.
For a few years we didn't have holiday as a family so we could cover all school holidays - actually we overlapped a week IIRC - and again paid extra for school holiday/public holiday cover. In some respects we were "lucky" in that DH job when the DC were small was almost shift work - every weekend and 1 or 2 days in the week free. And so on and so on. For a long business trip to Asia we paid for my mum to come to us for a week to cover. All expense and arrangements that we made to facilitate working.
I almost never mentioned this to managers/bosses because, frankly, the slightest hint that i might have any sort of responsibility outside the office sent them into a frenzy of doubting my loyalty etc. i was overlooked for promotion and bonuses despite long long hours (sometimes i took the DC to the office on Saturdays…) but in the end it paid off because eventually i did get promotions and bonuses because i had shown that i was dependable.
And my DH stepped up and did what had to be done too. We did it as a team. Frankly it was a huge PITA and i hated a lot of the extra mental energy we spent arranging stuff. But my pension pot is fine, i have a good job and my DC are none the worse for having had working parents.