Your eight-year-old is definitely old enough to make dinner with you. She can choose a meal she'd like to eat, and she can cook it herself for everyone (with your supervision). You can do this at least once a week, especially since you say they don't have any homework. That way she'll be learning to make food for herself as well as being involved with some menu planning.
Do you think it's cruel not to make children extra food if they don't like what you made? - Page 6
We used to play an m&m game. Three m&ms per child at dinner. The m&ms were earned for different things.Napkin on the lap, staying seated the entire meal, the adventure bite. When the behavior stuck, we'd rotate in a different one. Amazing what a kid will do for an m&m. LOL. We haven't done that game in a long, long time, and actually, I think we tried it once with my now 4 year old (because it had worked so beautifully with the older two) - but she quickly realized she didn't like m&ms all that much and they weren't worth the effort. I feel a bit conflicted about using candy as a reward - our potty training efforts ("potty training in less than a day") had a similar reward system and honestly, it bothered me. But it worked. So, I guess...I don't know. We aren't a dessert eating family, so three m&ms seem harmless. And I don't see any food-issues rearing their heads with my older kids bcs I used food as a reward...yeah, can you tell I'm a little conflicted about it? But I'll tell you, family mealtimes used to run a lot more smoothly when that game was in effect!
M&Ms don't exist in our house, due to food allergies/intolerances, so this approach wouldn't work. I know of families that use M&Ms as reward for schoolwork, too. Oh, well. Next idea?
If you want to do a positive reinforcement type thing, we've also used plastic coins they could turn in for rewards. Haven't used that for meal time, but it's worked on long car rides. Keep meaning to try the "caught you being good" coupons around the house, but haven't gotten my act together.