I was a mother's helper when I turned 13. I would hire a responsible, mature 12 yo I knew well.
I have a newly 15 yo who comes over to be my mother's helper for a few hours each week, she's been coming for a year and half. She basically just plays with G in one room while I'm in another actually accomplishing something. With a 12 yo I might not let them play in the front yard but anywhere in the house would be fine. I still change a diaper, get snacks, etc for G when he needs them. I pay her $5/hour and it's the best money I spend
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Wife to V since 5/19/07 my hard workin man
Mom to G since 8/10/09 my crazy 10 yo
Z since 9/10/13 my wild thing 6 yo
Surprise! N born 2/8/16 terrific 4 yo
*my help comes from the Lord above*