Might I recommend getting/ fostering a dog, and making it your responsibility? Dogs must be walked at least 2x a day. You can start with just down the street. The dog will want more, and they are hard to refuse. It can be a family activity, and with an average 8-12 year lifespan, et viola, an exercise program with built in positive reinforcement.
As for the food choices, can you start making changes each time you grocery shop? Sounds like you want minimally processed foods for your kids, eat the same yourself. When there are no oreos in the house, and your treat is another hunk of melon, I imagine everyone is a winner.
Also, to re-tool your diet/ reduce your calorie consumption, try the "eat half/ eat more" diet strategy. You split all of your regular meals in half, and precede each with a cup of water and a cup of something healthy/ low cal.
Your ordinary food day looks like this-
bowl of cereal and a short stack of pancakes, orange juice and coffee for breakfast.
a big mac, fries and a large soda for lunch
steak, potato and cheesy brocolli for dinner and apple pie for dessert.
Your eat 1/2 eat more food day would look like this-
a glass of water, two clementines a half bowl of cereal, half stack of pancakes, half galss of ok and half a cup of coffee for breakfast. an hour to an hour and a half later, you would then drink a glass of water, have a handful of almonds, and eat as much of the remaining 1/2 breakfast as you can manage.
for lunch, its a glass of water, something healthy and low cal like a cup of raw spinach, then 1/2 of your big mac etc.
wait an hour or an hour and a half and then drink a glass of water, a bunch of baby carrots, and as much of the remaining 1/2 lunch as you can manage.
the same holds true for dinner and so on.
This works by introducing healthy foods. Not creating a sense of deprivation, and by promoting gradual change and increased water consumption. At the end of the day, however, calories are calories, so you must make sure that you are actually introducing healthy, low cal options in the eat more arena; that you are not unwittingly increasing your portion size in the eat half arena; and that you are slowly eating less of the old foods as you get sated on the new ones.
Good luck to you and yours,
F. B.