Possible Close Encounter?

It was during my summer holidays when I saw it. I was round about nine years old and sitting on the swing out in my back garden. It was a lovely clear day and I was just minding my own bussiness when I felt like I needed to look up to the sky. When I did I saw two perfectly round white circles in the sky. Being nine years old I freaked out and ran into the house shouting and headed up the stairs to get a closer look out the window. As soon as I arrived in my bedroom I looked out the window up to the sky and they had vanished. It was only a few minutes that had past and clouds wouldn't move that quickly would they. I told my parents to look with me and they did not see anything. Since that day anything concerning UFO's and aliens makes the hairs on the back of my neck stand up.

Was it just clouds I saw or was it really a UFO?