The Magellanic penguin chicks hatched in May, and they've both been identified as females.
The sisters, currently known as Chick 420 and 421, are reaching critical growth and developmental milestones, according to the aquarium.
Shedd officials are asking the aquarium's members to choose names for the birds ahead of their public debut on exhibit next week.
Shedd Aquarium's members can cast their ballot online from August 11 through August 17.