Why do baby canaries die after 10 days?

Answer 1

They usually don't , If they do there could be many reasons.

Perhaps the mother is not feeding them enough or the father rejects them. It's not abnormal to have one or two babies die out of a clutch of eggs. Some get less nutrition than the rest and die from the others weight crushing them.

If they all die something is really wrong. You may not be supplying the parent birds with the correct foods. No matter how good the mother or father may be at the end of the day they can only feed the youngsters the food you give them. I breed birds and it's something I'm very careful about. Imperial440

Also remember that like all babies, they need to be kept warm and out of drafts. It's very easy for birds to "catch cold" even when they are older.