They eat millet like we eat chips!
(That's fries in US). It is junk food to them - a quick-fix mouth satisfier. That's not to say it is un
healthy but like all things should be eaten in moderation.
Your birds are quite young aren't they? So it isn't a problem yet. But continue to encourage new foods.
I would also remove the millet and let them have it only as a treat/reward.