No items in creative.

I'm currently in the process of building a parkour map. On that one specific world however, despite it being my world I can't access any materials in creative, where as my brother can. If I type '/give @p' into a command block, or in chat - the only things it'll allow me to get are different command block variants. I was hoping to get this map out during August but it currently looks as if it'll have to be postponed.