plan some meals that include some high protein and fat bits that the kids eat but you don't.
Like pasta with a non-fatty vegetable and tomato sauce, but the kids have it with a drizzle of olive oil and grated cheese, and you don't.
Also things like mashed potato, mashthe potato without adding any butter/milk/cheese for you, then add these things for the kids.
Bulk up on a starter of steamed veg or salad before the main, then just have a smaller portion than the kids.
Is this the sort of thing you are after?