Based on my conversation with Universal today, I agree with Phamton. We just received our tickets. We purchased 3 adult tickets and received 3 "children" tickets for free. When I looked at them, two things stood out. First, all 6 tickets looked exactly the same, and second, they did not have any documentation about expiring. The only expiration wording on them is that they expire 4 days after initial use.
I called Universal to ask about this. The girl said the 6 tickets are all the same, no adult or child designation. The way she answered the expiration question was very shaky. She thought that they didn't expire, but said to use them before April 30th "just to be safe". You could tell she didn't know the real answer.
I don't see how they could enforce the April 30th expiration unless there was some written documentation. Just my two cents.
Thanks,
Dan.