McCallen Park is both a park and the headquarters of the Boys & Girls Club of Huntington Beach(about which I know zilch). It's pretty much a pocket park, a nice bit of green tucked between streets. By the way, both appearance and the website linked above indicate that that tempting parking lot is for the club, not for people visiting the park, so streetside it is, if you're driving.
It looks like there's a setup for soccer, and there are a couple of picnic tables, though those are unusually beat up. I'm not sure I'd want to set food on them, or sit on the benches, without a certain amount of extra covering. The phoebes like them, though. In general, phoebes seem to find picnic tables to be useful for bug-watching. I've seen them on bench or table in several parks now. I suppose they do provide a clear, branch-free view and height at the same time.
There is a playground, but it is behind a fence. The gate was open and the walkway free and clear when I went through, but I have no idea how normal this is or is not.
Rstrooms? No. Water fountain: Likewise, no. Possibly people coming for the Boys & Girls club have access to both (I'd be surprised if they didn't, given that there's a whole building there), but it doesn't look like people just walking through do (Then again, I've never actually tried going through those impressive doors)