It typically works really well to give them a choice about part of the afair. For example, if they need to take a gross medicine, that's not an option. But it will go down a lot better if they can choose to take it with the blue or the red spoon, or to get a kiss or a hug afterwards. I also try to leave room for "rewards". For example, at dinner, the kids can take seconds of whatever they like best after they finish eating. However, I make sure to serve them at least a little bit of everything and make them eat that first, and save some of the stuff they really like for seconds.
how can you cause a toddler to do something that they don't want to do?