should I clean them?

[Chicken Ducks]

My chickens Are 15 days old, and some of the chickens look like they have bald patches. They also look dirty...which I guess is because of the chickens jumping over each other and dirt getting stuck to their fur.

Should I clean them or let them be?

 

[KountryBoy15]

Yes and rub grease on the spot tell gets better

 

[Chicken Ducks]

Grease? What sort of grease?

Can I use vasoline?

 

[farnorth]

A cheap tube of triple antibiotic is 88 cents at Walmat and has a petroleum jelly base. That would probably work for bald spots. But make sure they don't have lice or mites causing the bald patches.

 

[Chicken Ducks]

How do I check for that?

Also I live in Australia.

 

[howfunkyisurchicken]

Just part their feathers and look for anything crawling on their skin. You may also see signs of eggs if there are pests present, they usually like to lay them where things stay moist (like near their vents).
Are they bald from picking or are they still just growing in feathers? If its the latter, that's normal juvenile chicks stuff and is nothing to be concerned about. Also, chickens are dirty little critters, give them time and they'll preen off any muck themselves. How big is your space for them? If they're running over each other, it may not be big enough.
And, I wouldn't apply anything to their bald patches unless they're also accompanied by wounds. If you find parasites, treat them with Sevin dust or whatever your Aussie equivalent is. Make sure they've got plenty of space and they aren't too hot or cold. Good luck