After watching the show, I was motivated to change my ways. I threw out the junk food and then challenged my kids to give up sugar for 2 weeks.

Everybody ate healthier with no complaining. I do have one problem. My 12 year old daughter has always been very thin. She is 5 5 and weighed 105 pounds. She runs cross-country. My 9 year old daughter has always been heavy. She was 4 10 and weighed 102. After the 2 weeks, the 9 year old weighed 96 pounds (I also started biking with this daughter). Unfortunately, the older daughter lost 3 pounds. I tried my best during the 2 weeks to encourage her to eat a lot and it seems like she did.

She cannot afford to lose any more weight, but I am thrilled with the change in my younger daughter who does need to lose weight.

I also have a 14 year old who is at her idea weight and a 6 year old on the thin side.

How can I handle the different nutritional needs of my kids without always drawing attention to their differing builds?

I have had the same problem with some of my kids, a cross country runner and a swimmer. My solution was to send more caloric things in their lunch during school, ie.-peanut butter for their apples, cheese sticks, healthy granola bars, nuts. At home is a little more tricky because you don't want to call attention to things. I might add a little more to their plates or snack and if questioned say it's because they are older, taller, whatever. Hope that helps, it is tough having different kids with different needs.

I would stay on the right track. As on some of the other shows you have seen, even though a child is thin, he or she can be unhealthy nutrient-wise. Maybe her body was adjusting to the loss of empty calories. Maybe switch some of her dairy or cheeses to fuller fat kinds, add nuts and healthy oils. If she is a runner, she could also afford to have a few more treats. I say keep it up your doing great!

Shift your goals (and your language) from "losing weight" to "becoming healthy". It's not about being the right weight, it's about being healthy. You can be thin as a rail and a high fat, high sugar, high sodium diet is still unhealthy for you.

I would make an appointment for each child at the pediatrician to create a food plan that matches their particular "physical activities" rather than their build (which I think you're right not to draw attention to). You can tell them honestly that runners, swimmers, tennis players and mountain climbers all need to fuel their bodies differently because they're using their bodies in different ways.

Yes-I agree w/above. Shift the goal to becoming healthy.
My family and I were on the show. I have 4 children 3 overweight and 1 at ideal weight. The 16yr is at her ideal weight. But yet she is probably the most inactive. Before the show, she couldn't even bend over and touch her toes. When we started the show and eating healthy she lost 3-5 pounds. I was also concerned b/c she didn't need to lose any. But that was all she lost. I guess her body was just adjusting to the new foods and she has stayed the same weight.
So don't go buying the thin ones cookies and cakes to keep the weight on. That stuff is not good for anyone, no matter how thin they are!
I also wanted to add that I'm so happy this show has inspired you to make a change for your family. I'm glad we did the show b/c it really helped us but I'm also glad while helping our own family we are reaching out and helping others make a healthy change!!