Dilemma? What would you do?

My partners ex is obese and now his 2 children (3 and 5) are getting more and more overweight every time we see them. She moved 400km away 6 months ago, prior to that they were staying with us all the time. I'm a health freak, so when they were here they were eating really healthily and I feel this was stabilising their weight. Also, in our house we don't let the kids watch tv and play computer games all the time..... at his exes house they do a lot of that. Now they are booked in to have operations to have their adenoids out, which makes me even angrier as I feel their adenoids are being affected by their weight and a general anaesthetic is pretty risky for an unecessary operation. Do we have a right to say something? My partner and his ex are in mediation at the moment as she gets extremely abusive and emotional if she thinks things are not going her way. I'm guessing I have to stay out of it. What do you think? It's very frustrating, the kids look sick because all they're eating is junk food.