My son has been having piano for one yr +, same as your son and his situation is similar to your son too. However, I still insist him to keep on learning as I still recalled that when I was a kid like him and my mum asked me to learn piano, I just practise as told but I do not want to do it and later I used various excuses in order to quit. My mom let me quit in the end. Now, I feel a little bit regretful for not staying in that hobby.
Unless for those who are very talented in music, I do think that it is difficult to get the child to stay in the hobby. Music is a good brain training exercise and what I do now is try to arouse his interests like practising with him together, praise him when he has played a good piece of music. That worked and sometimes he said he would like to perform before my friends and relatives.