Oh I absolutely let them know they're just fine the way they are. All the way back to my grandparents everyone from our side of the family is tall and lean/thin. I've showed them pictures of myself and their mother from when we were younger, same as them. Very tall, lithe even wiry but perfectly healthy. They're quite confident in their appearance and ability, I'd like to think I've contributed to this by encouraging an active lifestyle as I feel nothing builds confidence like overcoming obstacles, meeting and exceeding challenges and expctations. Nothing makes you feel good about yourself, young or old, like deciding to hike up a mountain and, 1-2-6-10 hours later standing on top of that motherfucker enjoying the view.