If it is only the easter egg chicks having an issue, it is likely that they had an issue from the start specific to those chicks such as genetic, parent stock, incubation, or exposure to something specific for that batch of chicks, because deaths are within the first 10 days or so. They could be more sensitive to something in their enviornment, so more info on what is being fed, type of bedding, temps and brooder set up may help, as horsejody mentioned.
Since not all are affected, and likely not bacterial, antibiotics are probably not doing anything useful. Just creating resistant ones and killing the good ones, which you don't really want, because a healthy bacteria load will help their digestion and prevention of bad ones from taking over. In the future, unless you know there is a bacterial infection or high risk such as a bite or open wound, antibiotics probably aren't the best choice.
For now, I would isolate the sick ones to make sure they are not being pushed away from food and heat. Vitamins or boiled egg yolk may give them a boost in the mean time too.
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