Has anyone treated mastoiditis?

Yes, for sure. It is fairly common in children. Usually it can be treated with just a tube in the eardrum, but sometimes needs a bigger operation to drain the infection. Beware of doctors overcalling "mastoiditis" on ct or MRI scans, when all they are seeing is fluid in the mastoid. This is seen with any ear infection for a while afterwards.
Yes and why? Acute mastoiditis are not uncommon in young children. Chronic mastoiditis are more common in older children and adults. See an ENT doctor for work up and treatment.