Father of three and startup founder here.

In college, I burned out on normal coursework and dropped out to teach myself how to code instead. To support myself, I worked in restaurants. I found that working as a dishwasher was quite complementary to learning to code. It was tiring physically, but I ended each day in need of mental stimulation, so went home and coded all night.

Now, as a father, I've found there's a similar complementarity in some ways but not others. There's a huge physical component to parenting, and this is perfectly complementary. There's also an emotional aspect (sometimes 2 or even 3 cry at once). This can be complementary or not depending on how much emotional labor work required (usually very little).

The one area where both work and kids is exhausting is attention. A toddler demands a huge amount of attention, and performing at work does too.