I went back FT when dd was 5 months old (all the mat leave available at the time and an extra month unpaid), DH was also FT. When she was 9 months old, I started a FT Masters academic programme for a year (which meant essays being written every second weekend, as well as full weeks of lectures), then back to FT work.
We just juggled all the way through - including when DH was away overseas (the other side of the globe) for 2 weeks in every 4 for a period of 4 years in the last recession. And often both of us having international travel commitments and well beyond normal FT roles.
Dd went to Creche near our offices when she was small (so she commuted with us, was easy to get to if she was ill, or could come into the office with us if need be for a half hour at the end of the day (6:30) to finish something off before going home).
When she went to school, an afterschool club collected her and we had to be there by 6pm to collect her. So that was more complicated both from a timing perspective and issues with traffic on occasions.
We didn't have family living near us to help out - DH and I juggled a lot. If DD was ill, we'd see who had non-negotiable meetings, and do a lot of WFH before that was a thing, usually by one going in at 06:30, swooping over at lunch (in the city of dd was well enough for a car journey, but at home if not), and the afternoon person working until 19:30, and both catching up at home once she was in bed for the night. Luckily, we had at least somewhat understanding managers who saw we managed to reach deadlines despite it all, and that we put in a lot of extras when we needed to otherwise as well so they gave some flexibility back when we needed it.