For me at least, with 3 kids at 7yo, 4yo, 1yo... when I say "I'm tired" as an excuse for not getting to what I want it truly means both that i'm physically tired, and mentally drained. Between work and kids right now, I might get an hour or so per day of mental/physical downtime. Which is okay, because the stuff I'd like to do is like... reading tabletop rpg books and playing videogames and such. Which is all stuff I can do when they're older, too. The stuff that really matters is the stuff they're doing, playing and learning and all that. So I give what I have for energy to the three of them, since I can always catch my goals up later.