One of the great things about homeschool is that we have the time to wonder. Wondering will often lead to questions and questions lead us to try and discover the answer. Or, at least it should. I personally think its important for us to encourage wonderment in our kids, encourage them to ask questions and think about why things are the way they are.
One site I found very interesting for this is Wonderopolis. This simple site is one that you can visit each day to see what the new question of the day is and how it was answered. The questions are ones such as: How do you have a voice? Do animals play hide and seek? How hot is the sun? and more. Older posts are listed under their category so you could even visit the site to supplement a lesson you are teaching.
My best guess is that this site would most interest those in the elementary and Middle School age groups.