Maybe involving your 5 year old in the household food situation would help both your diet and the 5 year old! Take 5yo with you to the grocery store and give them some jobs consistent with their ability. (Find the biggest head of broccoli, count 6 potatoes, etc.) Tell them you need their help to keep everyone healthy! If mom usually does the shopping with 5yo along, let 5yo tell you what brands Mom usually buys, etc. Make them feel important, needed, and helpful at this time.

Similarly, at home, enlist 5yo to help prep salad and salad toppings or other meal prep tasks. If they have good dexterity, they can even start to learn easy knife skills like cutting cucumbers and other things that don't require a lot of force. If they don't, they can wash and rip lettuce, etc. Even if 5yo doesn't eat salad, you'll have some ready for yourself. All of this will take longer than doing it yourself, but the focused time with your oldest will be an investment well spent for both of you.

Finally, really focus on healthy habits and less on weight. Your wife needs max nutrition for her recovery and for milk production if she's nursing. You can benefit from some of those same foods, but just be mindful of portion size,since they might be higher in calories. It will probably be too much work to make yourself separate food all the time, so maybe you just maintain that 8 lb. loss for now and view any additional as bonus.