Loop Cocoon™ baby earmuffs fit head circumferences from 40–56 cm, covering ages one to four. If the strap is at its tightest and still feels loose, they may need a little more time to grow into them.

Otherwise, the FitGuide is your friend here. When it lies flat, the fit is right: properly positioned without overtightening. Too tight? Undo the straps and start again, adjusting little by little until the FitGuide lies flat. Don't go tighter than flat. Too loose? Same thing. Readjust until the FitGuide lies flat and the earcups sit snugly with no gaps.