A toddler who is told to share their favorite toy with another child, even if they don't want to, will probably show their reluctance by doing so in a begrudging manner.
You can use the word begrudging to describe anything that is done unwillingly or resentfully. For example, if you help someone but secretly wish you didn't have to, you're helping them with a begrudging attitude. This term often describes actions done with resentment and a lack of enthusiasm, typically because you have to do them, but you really don't want to.