When I bought my second mini they had her saddled up with two (fairly big)kids riding her around the ring
Poor baby was also nothing but skin and bones. So my little 3 yr old is "broke" but she'll never be ridden as long as I own her. I don't think just sitting a kid on her and leading her around would harm her but what she was being used for was NOT good! She's definitely not big enough to be packing all that weight! They probably had over 100 lbs on her and she's only about 37" and is pretty fine boned.