L.H.
I don't think I used my actual bumper until my son was past 10 months. Until then, I used a mesh "breathable bumper" (http://www.toysrus.com/product/index.jsp?productId=226684... keeps them from getting arms/legs caught in between slats, but allows them to still breathe if they roll up against it. Will be buying one more for use with my twins due in August.