Lighting

[Jpat]

They grow like crazy

 

[Soon2BChixMom]

Pekins grow fast regardless, but if you get them off the heat they will feather faster. As long as they habe a way to get away from the heat lamp they will do well too.
You should do some reading on the care for ducklings. There is a sticky here in the duck forum as well, I recommend Storey's guide to raising ducks. There are a few other good poultry books recommended on byc that would be beneficial as well.
https://www.backyardchickens.com/threads/raising-and-caring-for-ducklings.750869/