Mums and other carers of formerly obese kids, how did you get them to a healthy size??
A few days ago I put DS's height / weight measurements into the NHS child BMI calculator and it says he's on the 98th percentile and morbidly obese. Am ashamed and really upset. Feel incredibly guilty. I thought maybe he had some "puppy fat" but never thought he was that large. How the fuck do I get his weight down??? I don't (obviously) want to shame him or tell him he's on a diet but have made a few swaps / changes. Would really appreciate ideas. Have instigated a fruit and veg chart to get him to eat 5 a day. He has a tendancy to sneak foods so had already hidden chocolates, biscuits, etc. He always has tea at 5pm, then has a supper which always includes a glass of milk at bedtime which I have switched to skimmed (these timings are pretty non-negotiable, he is being tested for ASD and routines are v important to him). He always has breakfast which is a brioche bun or two.
His dad and I have split up and it is very acrimonious; I can't discuss this with him as he will blame me, report me to the social etc. I know that when he's at his dad's (which is 50% of the time) he does eat a lot of junk food and sweets / candy. Not trying to point fingers this is just for context for anyone reading.
For further context, he doesn't drink fizzy drinks and isn't that keen on juice, has mostly water to drink so can't do a switch here. He plays sport twice a week but cub scouts which is mostly running around so he is active.
Do I need to get a dietician involved? Will he grow out of it? More water? More exercise? I was a skinny child and I feel out of my depth. He has had one child tell him he's fat and I don't want him to be bullied.
Please be nice to me if you reply... I feel fucking terrible 
thank you in advance xx