I started being at the barn all day unsupervised in the summer from about age 13, when I got to lease a horse for the summer. I somehow managed to stretch out grooming, tacking, riding, untacking, bathing/cooling out, grooming, cleaning the stall/buckets/setting feed/throwing hay, cleaning my tack, re-organizing my tack box, hand-grazing, sweeping the barn, etc., that i still wasn’t done when my mom came to pick me up. There were lots of other girls my age doing the same, though, so we had each other there, and we never really got into any trouble (although I realize now we probably should have let an adult know when we were going on long trail rides off the property).
8 years old is too young, though, I think. My sister was probably 9/10 when I was there “watching” her as a 13/14 year old.
And we always packed a lunch.