I had a three year old and a 5 month old when I went back to work as a single parent. It was a long time ago (kids now in their 20s) but I do look back and think that was the easier time! But that might just be selective memory!
I had a brilliant childminder who lived across the road from me. I had some older teenagers, young adults who the kids knew through church and clubs. If I was working late, one of the older kids would collect from the CM and take the DCs home. My only real issue was summer holidays as my CM took almost a month off. Two years I had a student nanny. My parents lived 200 miles away so they could go there for a week at a time (but not for just overnight)
CM had kids same age and all went to same school so that was easy as well. I had a spell where I worked mainly from home and kids still went to CM.
What I found harder was when my two wanted to do different after school activities so DD2 wanted to go to rainbows but DD1 and CM's DD1 went to gymnastics. I did have to rely on friends which meant building up a favour bank!
The hardest time by far was when they were teenagers, no childminder, no real solution apart from just trusting them not to burn the house down between finishing school and me getting home. Thankfully I had a job just five minutes away at that time but it was still a worry.
The downside would be no time for yourself; weekends were laundry/housework/shopping and never being able to go for a drink after work or commit to social events.
We had a lot of fun though and are probably much closer as a result.