Are bones hollow or solid?

No, all the bones are not solid. Inside the bones, there is gooey stuff called bone marrow. Bone marrow makes red blood cells, white blood cells, and platelets. These cells go into our blood and help our bodies to be strong and healthy. Do you remember what these blood cells do? White blood cells help us to fight infection. Red blood cells carry oxygen around the body and platelets help us to stop bleeding after an injury.