I have kept several preschool age children while Mom was at home on mat. leave with the baby.
I did a 3 day a week minimum, and set days. Both moms couldn't afford to go back to work after number 2, but the older ones stayed about 6 months to give Mom a break. It's impossible around here to find kids over 2 years, so some income was better than none for me. To each their own...