Many children have male siblings, both older and younger. Teach your baby the sign for the word brother in baby sign language with the following description and video.
Hold one hand in the shape of the letter L in front of the chest with the thumb pointing up. With the other hand, begin with the sign for boy. Form a flattened C shape with the thumb and fingers. Open and close the fingers in front of the forehead to mimic the motion of grasping the rim of a baseball cap. Then form the hand into a signed letter L. Tap the second L on top of the first L.
Beyer, Monica. 2006. Baby talk: A guide to using basic sign language to communicate with your baby. New York: Jeremy P. Tarcher/Penguin.