Holds food in mouth

My grandson has just started a new behavior. He will eat his food than towards the last few bites not swallow them but store them behind his front teeth. My daughter and I have asked him to either swallow the food or spit it out but he refuses. We have given him something to drink hoping that would dislodge the food and make him swallow it but it hasn't helped. Brushing with a toothbrush hasn't helped either. We end up having to put our finger in his mouth to get it out. We are afraid of tooth decay and possible choking. Any suggestions?

[Zoelula]

You might want to speak to his pediatrician about this behavior. This is an eating disorder board.