Punching Bags For Littles

Do you know those punching bags for little children? They have sand in the bottom, inflatable, made of plastic? I want one for Baby D but there's one thing I don't understand - WHY do they have their heroes on them? To punch out the good guys?! Dumb idea. I wonder if I can make my own though that leads right to 'what should be on it'? No faces I would say, I'm not trying to teach him to punch people. But he's all into punching. Maybe I'll get one of those balloons with a long rubber band handle and attach it to something for him. Or suspend a pillow on some sort of a frame. Much better idea I think.