Could it be the texture or what it is prepared with?  Different cooking methods can give the chicken a different texture, especially the outside.  Poaching a breast in water, chicken stock or other sauce will give it a very soft texture, sautéing can give it either a hard or soft outside but soft inside depending on if you brown it and to what extent, baking or roasting can give crisp outside and soft inside.  

I have a couple of chicken recipes on here.  Homemade chicken “nuggets”, Moroccan chicken, chicken with mushrooms (like Coq au Vin), roast whole chicken.  Just search for key word chicken.

Have you tried roasting the chicken so that the flavors are infused but not overwhelming?   Try with something plain and quick like sautéing a cut up chicken breast or tenderloin with simple salt and pepper and then work up to more complex flavors.  See if that makes a difference.  Lemon and thyme are good starts as they’re not overwhelming but add a nice taste that most children would like.

Also try your own idea of blending it with rice.  You can even buy ground chicken (or grind your own) and make chili, burgers, and meatballs.  If he’s able to eat directly from the bone safely, a drumstick is great because they have fun while eating with their hands.  

Good luck! Let me know if any of it works.