You can find Qatari dresses for Girls and Boys both at Souq Waqif.
Rounaq is located near Souq Waqif, near Fanar Islamic Center (on the other side of Bank Road). Another branch of Rounaq is located on the Airport Road going towards Wakrah.
Yet another branch is located near Town Center (behind KFC) in front of Al Ahli Hospital.

Enjoy the National Day :)