It’s possible to have both kids and side projects, just involve them. I used to hang around my dad’s shed doing random stuff when he would do his woodworking side projects, and sometimes he would show me cool things and let me cut wood. It probably helps though if you have the “right” kind of kid for this stuff.
I was thinking in the context where you'd like to potentially monetize the side project as some point. But definitely, I spend a lot of time supporting my son's Minecraft obsession, and since he's already expressed great interest in building mods I think that's something we'll do together that could be considered a side project.
In fact... I see a possible future where I have a collaborator worth his salt :)
