My husband is 6-4 and about 250 lbs (as of this morning, I weigh less than him! woot!). He could stand to lose a bit, and he eats like crap, but when I met him and he weighed what the weight charts tell him to, he looked way too thin (and he was - he didn't have much money and wasn't eating nearly what he needed to). My 9 yo ds is about 4-6 or 4-7 and around 66 lbs of lean muscle. Seriously, I could not pinch an inch on that child and he has a 6 pack and has for years. He's very strong and runs around like a hyperactive chicken with it's head cut off

. He really doesn't eat healthfully at all, buthe has some special needs that contribute to him being very, very picky. What he does eat is generally healthful, but he has whole food groups that have been stricken from his diet. He pretty much lives on whole wheat bread, cheese, and water. 6y8months yo dd is about 4-2 and around 45 lbs. She's also thin and very tall for her age, but not nearly as active and much more physically tentative than her big brother. She reminds me of me in that respect. She will eat practically anything and her favorite food is beets. She's likely to hit the veggie tray at a party before even looking at the cookie tray. Ds2 is 4 and a half and tiny. He's about 38 inches tall (3 foot 2) and 32 lbs. he was a preemie and has always been small. He's a very active little guy with a HUGE sweet tooth that I have to keep a close eye on, but he eats a wide variety of foods and loves lots of different veggies and fruits.
As for my family growing up - my mom yoyo dieted for years (putting me on them with her. ugh) and then spent a lot of time hanging out at well over 200 lbs (at 5-2). In the last two years she's very slowly lost about 60 lbs. She's still not at an ideal weight, but much smaller and healthier than she has been in a long time. My brother is one of those magic metabolism guys and eats like a horse (even now, at 43 years old) without gaining an oz. My sister was always thin growing up until she had my niece, and she has been yo yoing ever since (and niece just turned 22). Right now she's heavier than her ideal weight, but looks way better than she did a couple of years ago when I seriously thought she had an eating disorder - she lost so much weight, so quickly, he teeth looked horrible, her skin looked lack luster, she looked gaunt, etc. I don't know how much she weighed then, but it did not suit her at all.