Picky Eater

So my 3 y.o has a very limited appetite. When he was younger he ate almost anything except veggies. Now literally all he eats is plain pasta, rice, yams, and chick-fil-a. Every now and then I will make a veggie juice so that he gets some type of nutrients. He takes a multivitamin everyday. I just don’t know what to do about broadening his meal choices. I try to put things on his plate to see if he’ll try it but he will NOT even think about trying new foods. Has anyone else experienced this ? Does anyone have any suggestions ?

P.S. he does have an appointment coming up with a developmental pediatrician due to speech delay. I will mention it to the doc to see if there’s a possible concern for autism (I know sometimes they can be picky eaters) .