I have used the 10 ride for my whole family every time on the Surfliner. Always purchased from the agent on duty at San Juan Capistrano with full knowledge of how I'm going to use it. No conductor has ever said anything when lifting the tickets either. It is even cheaper than getting child...
If it was me, I would do the Surfliner round trip to San Diego. Most times the same train sits at San Diego for 45 mins then comes back up. Way more scenery. I guess it depends on whether you want to spend the whole afternoon/evening on the train or not.