The collared-dove (Eurasian) feeds primarily on grains, seeds and the occassional insect.
Adults regurgitate what they've eaten to their young. By the time they do this, it's mixed with an immune system boost that comes from the adult's body and of course, it's partially digested.
If you want the best for adults with young, offer them cereal grains (wheat, oats, corn, etc), an assortment of seeds (dove mixes can be found at many pet supply stores) and make sure they have fresh, clean water available. Rather than mess with the insects, which aren't always eaten, let them decide when to add this to their diets.
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Many have forgotten this truth, but you must not forget it.
You remain responsible, forever, for what you have tamed.