Help! I tried different foods, but my son just wants to eat cer

My son is 4.5 years old, and he is a picky eater. Although we mostly serve organic whole wheat cereals, pan cakes and snacks, he does not eat much vegetables and proteins. The only vegetable he sometimes eats is broccoli, and occasionally he eats chicken or turkey breasts or fish fillets. He drinks a lot of organic chocolate milk and sometimes he asks for cereals three times a day.

He does not like Chinese foods, and once a while, he would eat hot dogs or pizza in the restaurants.

Any advises?