My great-grandmother, an immigrant born in 1892, never referred to her great grandkids (and I assume the generations before us) as children, toddlers, or the like. We were called wee-littles, lassie, laddie, or laddie-buck at any given time. (Never lassie-doe, though!) My granddad, her son in law, called us kiddies and kiddos, and the boys were sometimes referred to as boyo as well. My absolute favorite of his, that he only used when referring to us grandkids as a mix gendered group, was fidgets. As in -- "will you fidgets quit picking all my strawberries?!"
Niblings is new to me. Not sure how I feel about it, it sounds very close to Nibbler (from Futurama).