An open letter issued Friday by the families complains bitterly about postponements. Also, they object to some defendants refusing to attend preliminary hearings.
The May 28 blaze killed 19 people, including four child care workers and two firefighters, at a daycare facility owned by the daughter of Qatar's culture minister.
Qatar investigators have blamed faulty wiring for starting the fire and cited shortcomings in safety planning by staff at the country's biggest mall.
The children killed were all members of Qatar's large expatriate community, including triplets from New Zealand and three Spanish siblings.