My mama budgie stopped feeding 26-day-old babies. Is this normal?

Budgies will typically eat a portion of their own food, and then regurgitate it to the babies so it can be more easily digested by them. If the parents aren't feeding the babies, there are commercial baby bird foods available that when added to water, mix up into a slurry that is easy for the baby bird to digest (since we can't regurgitate to them!). As the babies grow and start to explore on their own, they will begin to eat the regular adult food as well.

If your budgie's parents are still around they will most likely care for them on their own. However if the parents aren't around or aren't caring for the babies properly, you will need to start feeding them yourself. Most pet stores will carry a basic baby bird food which has feeding instructions depending on your bird's age. You'll also need a syringe with which to mix and feed the food. As your bird grows you can start introducing an adult balanced diet to encourage them to begin eating more solid foods.

It would be hard to tell what caused the babies to die without a necropsy/examination. It's possible there was a genetic issue, an illness, or the babies were just weak/not fed as well and so passed on. Your parents are a bit young still and may be having trouble caring for all the babies, so helping out by supplementing with baby bird food may be best to help the remaining babies thrive.

Momma bird may be a bit stressed out now that there are new babies to care for. Adding in extra food and water dishes so that each bird has one to eat at without fighting, and making sure both birds have their own perches to relax on can help reduce tension. As for the babies, momma bird should care for them herself, however having some commercial baby bird food (most pet stores will carry it) can be useful in case she can't care for them all on her own. As they get a bit older and start to explore, you can start to offer treats and pets to get them used to being handled.

It'll probably be a few weeks before the babies start emerging from the nest. Baby birds tend to be born without feathers and are unable to walk around or move much, relying on their parents for care. Once they begin to grow in size and get more feathers, they will likely begin to explore a bit more.

Provided Boo Boo is still eating, drinking and flying normally and provided she is feeding her babies, I would not be too concerned. However, if she becomes lethargic or if her appetite decreases, I would recommend she be seen by a veterinarian who is familiar with working with birds.

18 days old is still a bit too young for a pigeon to be on its own, so the parents should be still caring for it. It's possible that the other baby is ill, or the parents ARE still caring for it and you just aren't catching them in the action. If you feel the baby is truly sick, injured, or not being cared for by its parents, then seeking help from a local wildlife rehab center is best. Do not attempt to move the baby or care for it yourself as it could still very well be cared for by the parents.