The more I read, the angrier I get.
Just appalling that these men have their children for limited time and can't be arsed to look after them properly.
Thankfully my ex tries bloody hard. I sent him a list of meals the children enjoy that he can very easily make or buy from Waitrose. I did him an online shopping order early on, and he refers to that (chicken kievs, grilled salmon in tortillas, loads of veg and fruit etc).
He tried but there's no escaping fact that they do eat more junk than with me. I just counter it but when they're back with me, I will ensue for a couple of days their diet is as pure as the driven snow. Thankfully they love all types of food, so as yet they haven't clocked what's going on.
Have you thought about spoon feeding your ex on this. As difficult a pill as that might be to swallow. So, next time you drop off/ he pick up, you could hand over a small bag of shopping with some microwaveable veg in it, so he doesn't even need to get a saucepan out, and a couple of healthy very easy meals.
Yes it will cost you. Yes it's pathetic that he needs this BUT the bigger picture is that potentially you're children will have one or two healthier meals, rather than a treadmill of shite.