Wooden stool, a little wonky (Elmstead BR7)

The stool is otherwise in good condition, a bit worn, but the cross pieces between the legs occasionally pop out, and I have not been able to stop this happening. The suggestions on Google are beyond my DIY skills. It has never looked like collapsing, and is fine under my six year old granddaughter, but I do not like to let a full grown adult sit on it.