Break is signed just like broken, which looks like you are grasping a stick and breaking it in two. The sign starts with both hands as a fist side by side and horizontal, then you move both fists out and twist them so they are aligned vertically.
When babies or toddlers play with toys, or household items like cups and plates, the occasional break is inevitable. You don't need to make a big deal out of breaks, so that your baby doesn't become shy about handling anything. However, you do want to be matter-of-fact that the item is broken and is not coming back, so that your baby realizes that it is not something they want to happen again, and they'll be more careful in future. The same signs break and broken also apply to bones -- but hopefully, you will never encounter such mishaps that will necessitate an emergency visit to the hospital.
One of the main goals of Baby Sign Language is to equip your little one to convey concepts that can be frustrating. We like the sign for broken because it equips your baby to let you know that something has gone wrong. Our little ones love to use it when they are trying to let us know about a toy that does not work.