Good news, first-borns … You are smarter than your siblings. Yep, researchers at the University of Edinburgh and University of Sydney found that first-born kids are the brightest of the bunch. Sorry, middles and babies … Researchers theorize that first-born babies get a lot more mental stimulation from their parents than other siblings. Basically, the first child gets much more of their parents’ undivided attention and are subjected to interactions and tasks that stimulate brain activity at a much younger age. That early mental stimulation results in better thinking skills and higher IQ test scores than subsequent siblings.