As can be expected, National geographic publishes material for kids with amazing photographs. I also like their simple, short text which makes for great read alouds. Sometimes we read so many stories with kids, we forget how much they love nonfiction.
Here are a couple of my favourites:
Kids ask why all the time. Here is a great collection of why questions and answers.
In addition to the Ultimate, there are three of these gems in a nice square format. They make a great gift. they could also launch some research or writing your own weird but true facts.