I get organic baby food since jars are so small and the food is runny. You don't want spices or additives (including sugar).
If the laxatives don't work he may have problems related to the fall, not the mealworms. Will you be able to get him seen?
You can offer him appropriately sized worms, like black soldier fly larvae (calci, repti or pheonix worms depending on your location) silk worms, or hornworms. You may need to order them online or have a local petstore special order them for you. Roaches (most use dubia) are good as well but are not permitted in Canada, Florida and by some parents/spouses.