Won't eat potato or pasta!

[CW34]

Hi,
My son, who is 22 months, will not eat any sort of potato unless it is processed (i.e. waffles or chips), he also won't eat pasta and will only pick at rice. This makes deciding what to have for dinner quite hard. He sometimes eats couscous but it depends what it's mixed with. He has what we have and we always put potato/pasta/rice on his plate - any suggestions to how we get him to eat it?
Thanks