Candidates generally travel the country holding fund raisers that they attend. If you attend one of these fund raisers, you get a little party out of it plus you'll probably get to have your picture taken with him. If you like the guy that much, I imagine you'd find that fun.
As for 18 year olds, I'm not a 100% about this, but don't give him money in your kids names. Bad idea.
Brief hijack for the fundraising for the rest of the field in the 3rd quarter only:
<font class="small">Code:</font><hr /><pre>
Clinton $28 million
Obama $20 million
Edwards $7 million
Giuliani $11 million
Romney $10 million + $9 million from his personal funds
Thompson $9 million
McCain $6 million </pre><hr />