L.
I have a 10 month old who usually pitches a fit whenever I put him into his high chair to eat and also is not wild about eating very much (although he's not picky, really). I have found that giving him toys to play with while he's sitting there distracts him and calms him down - enough for me to feed him, and he doesn't mind at all then - lets me feed him the whole meal. I am not at all familiar with what 21 month olds are like, but maybe that would work for you. Blessings to you!