[throwaway318]

Take an hour for yourself everyday.

Do some exercise like situps or skipping early in the morning; have a pullup bar across a door frame to use when the kids are brushing their teeth, and some pushup handles. Much more time effective than a gym unless you're really into something in particular.

Do whatever they like in the evening, get engrossed, forget forgetting your work, forget yourself. Their time is fascinating.

Edit: Get an early night. Enjoy doing even more tomorrow, today's done with.