Chicks shaking their heads
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It could be something or nothing. I'd suggest adding vitamin supplements / electrolytes to their water and see how that goes for a week or so before trying antibiotics - it may be something other than bacterial. The vitamins should help give their immune system a boost, so it should help them get over whatever it is. As long as they are fine and healthy in every other way (eating, drinking and acting normally) then i personally just let their bodies deal with it.
This is just based on my experience - I'm sure other members will offer other advice - go with what feels right to you.
All the best
Are they scratching their heads excessively? If you can't see any evidence of mites / lice then maybe not.
My chicks tended to shake their heads often when they were growing in their new feathers. I wouldn't put lice powder on them, unless I visually could see evidence of lice, eggs, or mites. Here are some pictures of what to look for, and they are better seen near the vent, around the neck, and under wings, depending on the kind of lice.
lice eggs feather mites