Our son has quietly stopped touching his grandparents' feet, and my mother noticed first

My parents were with us for a week. At every hello and goodbye, our son, who starts class 9 in June, gave them a hug or a namaste and moved on. Two years ago he'd bend down without thinking. My mother didn't say anything to him, but she asked me later if he was upset with her. When I asked him, he said it felt 'like a show' and he'd rather hug them properly. I don't want to force it, and I don't want my mother hurt either. Has anyone found a middle path, or did you just let it change?