At buffets, under 3s are free. Most of the reports I've read say that they weren't even charged for drinks for little ones.
At plated restaurants, the assumption is that the toddler will share from a parent's plate, or in our family, an older sibling's. You can order a kids' meal if you feel it necessary, but you'll have to pay OOP for it.
We've found Disney portions to be very sharable, and food sort of gets passed down. DH & I share with DD8, who is interested in trying adult foods, and she shares with DD1 because after trying our meals she's much too full to finish a whole kids' meal anyway. DS11, aka the bottomless pit, is the only one who generally eats his own meal without sharing more than a tasting bite or two.