Ok. So you've thought up all sorts of games, you're encouraging like crazy, you're allowing your child to take some control of what activity will happen next, and things still aren't going well? Here are a few more ideas!
Change your practice time.
Some kids really like to play after school, but can't focus before bed. Others would love to have an excuse to stay up just 20 minutes later but are too tired and hungry right after school. Some kids want to stay in bed as long as possible, while others are at their most awake and are ready to focus at 7am (if you're lucky!). Work with the schedule that seems the best fit for your child.
Have multiple sessions in a day.
Break up your 30-minute practice session into 5- or 10-minute increments. Work on a different task in each session. Variety is great for staying focussed, and you can do some really fun things in your breaks, too. Who wouldn't have a good time dancing to a recording of the piece, singing silly words to the music, drawing a picture inspired by the tune, seeing if you can clap and stamp out the rhythm of the melody or seeing how long you can stand on one leg before the next session starts?
Set specific goals for each practice session.
Have one thing you're trying to accomplish for each mini session. It can be as simple as clapping a rhythm accurately with a metronome or as complex as mastering half a piece, but choose based on your child's skill level and the amount of time you have in that single session. You want them to come out victorious so they want to do more next time!
Make the instrument easily accessible.
I always play more when I have a flute close to hand. Keep the instrument somewhere safe, but just as easy to get to as a toy or favourite book, and your child will be more likely to pick it up to play for fun, too.