This is a noteworthy article on the potential harm of putting children on diets. It backs up my own experience that getting kids to move more and tune into their bodies – to only eat when hungry and stop when feeling satisfied – is a better approach. It’s empowering rather than demeaning and teaches them useful skills they can carry into adulthood.
A reasonable goal for overweight or obese primary school age children is to stay the same weight for a year and catch up by growing taller. Take them to your GP a couple of times to check their growth rate is not affected.