I'm not sure why you'd want a 10 year old "active" child to lose weight.  Children typically gain weight prior to "growth spurts" and this spreading and thinning is normal.  If you are concerned that your child is overweight, then a couple of ideas come to mind:

1).  Aerobic exercise for 30 to 60 minutes each day

2).  Eliminate snack foods and high calorie juices.  Substitute fresh fruits and vegetables.

I'd recommend the book, "Healthy for Life" by Dr. Ray Strand as a basis for these recommendations - good science and the strategy works.

Peace,

Daniel A.