Some 100,000 years ago, an extended family of 36 Neanderthals walked along a beach, with the kids jumping and frolicking in the sand, scientists report after analyzing the beachgoers’ fossilized footprints in what is now southern Spain.

“We have found some areas where several small footprints appeared grouped in a chaotic arrangement,” said Eduardo Mayoral, a paleontologist at the University of Huelva and lead author of the study, which was published online March 11 in the journal Scientific Reports