STORY: The opposition civil defense service said three children and a woman were among those killed in the strikes on the crowded camps where more than 70 people were wounded and rushed to field hospitals.
Video released by the organization on Sunday showed an injured man with blood on his clothing and a baby being helped into an ambulance.
War planes flying at high altitude, aided by Syrian army artillery, also dropped bombs on forests near the makeshift camps west of Idlib, witnesses said.
No immediate comment was available from Russia or its allies in the Syrian army, which says it targets the hideouts of insurgent groups and denies attacking civilians.
More than 4 million people live in the densely populated opposition-held northwest area along the Turkish border. Most of them were driven there by successive Russian-led campaigns that regained territory seized by rebels.
Opposition sources said a coalition of armed groups led by the jihadist Hayat Tahrir al Sham organization and another led by mainstream Turkish-backed rebels retaliated by attacking several major Syrian army outposts in the region.