Coaches stretch kids at DD's gym. I've seen tears, and mostly it's because kids are inclined to stop at the first pull they feel, not knowing they can push themselves further and that honestly it's supposed to hurt a little. DD is like OP's kid, VERY strong, lacking in flexibility. Dr. even remarked she has the strongest abs on an 8 year old he's ever seen. But she struggles with splits and shoulder flexibility. Her knees often look bent when her leg is totally stretched out, so she definitely has tightness issues. A stretch I've seen that sometimes results in tears is on designed to get her splits where she sits on one knee and wraps her arm around her coaches legs (behind her) and coach lifts her other leg as high as she can tolerate while it's straight. Hard to explain, but it's like oversplits - it hurts and they're at the end of practice and they're tired and hungry and so they cry. It doesn't bother me because I can see she's not being hurt, she's just being pushed past comfort. I also see the holding their arms up and back while they are in splits.