Friend's 3yo has down syndrome. Doesn't eat most foods, only pasta. Will he outgrow this? Would therapy help him gain better control of his tongue?

Yes. Occupational therapists as well as speech therapists can help children with textural issues and oral-motor control problems. Both therapists should be involved with children with down syndrome starting in early infancy. A nutritionist with experience in pediatrics would be highly recommended in this particular child in addition to the others to help mom plan a balanced diet.
Yes. I agree with first answer. Children with downs syndrome need ot and speech. The extra chromosome also affects their digestive tract. I encourage all my patients to look at nutrivene supplements (nutrivene.Com) started by a mom of a child with downs. Also research changing minds foundation- an excellent resource for downs information.
Need Help. Children with down's syndrome have multiple health issues and sensory processing disorder and one of them is eating, he will need to try different textures and have his occupational therapist work with him on this .Otherwise refer him to feeding specialists.