Your chicks are way too young for sunflower seeds and bird seed. Wait until they're at least a month old for bird seed, and a few months old for sunflower seeds. At this age it can cause crop issues even if you provide chick grit. For the record, even when my chicks only get feed and crushed hard boiled egg, I still give them chick grit at least once per week. I do this because I've had a few broodies raise chicks and have learned A LOT from those mama birds. At just 3-4 days old, mama had her babies eating grit, and I firmly believe that mama knows best.
Hard boiled egg is fine to feed your chicks, but not daily, especially if they're store bought eggs. If you think about it, egg is their very first meal, courtesy of the egg they developed from. In the last days before they emerge from their shells the chick will absorb the last of the yolk, which is what makes it possible for hatcheries to ship live chicks. But beginning at about 1 week and increasingly as they age the chicks will require a broader spectrum of nutrients. While the protein in the egg will be outstanding for feather development, getting too much of it can deprive them of the other nutrients they need for better, comprehensive development. The same holds true with meal worms and other treats. I'm even wondering if all the egg could be contributing to the pasty butt issue.
