Same here, I can herd the chicks a few feet away from the run but then they start flying over them or just running around and screaming. But if I can get them to where the adults are, they'll join in and forage, so it's a matter of trying to get them out there in the first place.
I've never had an issue with a chicken eating a poisonous bug (or plant) - they seem to err on side of caution in not picking up bugs of certain colors or shapes... not sure how they know but they just don't do it. So I don't have anything on hand for such an event.
A lot of useful first aid stuff is the same as humans or other pets would use - vet wrap, neosporin, vetricyn (which I even use on myself), epsom salts. Anything more specialized I'd get as needed, as expiration dates are something to always keep in mind.
Well... with no adult chickens and the ability to run power out, day 1.
Otherwise I wean off heat at 3-4 weeks and they get locked out of brooder at that point.