Don't worry too much about the result, just take it easy. To perform on stage is a very good experience to the children. He could perfrom much better if you let him to have more chance to consolidate his perfromance. He can also know his strength and weakness and then build up his self confidence. Don't give up!
Hey, treat it as an experience. He'll need so many chances like that to be perfect (when he becomes experienced and not so nervous). You have to believe in him and keep practising. Keep going!