I found a round blue pill in my sons room with the name alva on it, what is it?

More than likely it's Diurex, a pill to help you drop water weight:

Water Pills | Diurex | Walgreens

But you should always consult a pharmacist about unknown pills, in case it's something made to look like Diurex.

Possibly take it to your local pharmacist and let them advise you to what it is...