I think you should be able to simply give your passes to the CM at the entrance to use them - I don't think you have to convert them to a different media.
The child upgrade question is a little trickier. According to allearsnet.com, if your child has just made the change from child to adult (i.e. is only 11 or 12), you do not have to upgrade your passes at all. If the child is now a teenager or older, you'll have to go to GR and exchange the child passes for adult passes. Apparently, there is no extra charge.
One note - the piece on allearsnet specifically talks about park passes, so I don't know whether there are any other issues associated with "pluses" since Disney doesn't attribute any dollar value to these under the old ticket system.