I shoot HS swimming on a regular basis. It's a challenge to say the least. Hopefully you can get on deck but with it being the state championships, that might be out of the question. In Texas, the UIL will only allow credentialled photogs on the deck. As Master Mason mentioned, more reach will most likely be needed than the 50mm. I typically shoot with the 70-200 f/2.8 which is a perfect match for swim meets. But, you'll also want to get some candids of the kids as well, so a shorter focal length will still come in handy. The 50 f/1.8 will be great for that.
The main challenge though will be the lighting, both amount and quality. In poorly lit natatoriums and since I know I need to freeze the action most of the time, I typically shoot in full manual and set my shutter speed at no less than 1/320, and something around f/3.2-3.5 if I can get away with it. Even though the 70-200 is wonderful wide open at f/2.8, I still feel more comfortable stopping down a bit for as much sharpness as I can get. Then, I'll sometimes use auto-ISO and just let my D300 choose the the ISO up to 3200 or so. I regularly get properly exposed shots that are very useable shooting this method. I do this because while walking around the pool, the lighting is constantly changing but I don't want my shutter speed to change. In adequately lit natatoriums, I might go to aperture priority and an ISO set at 800-1250 as long as I know I'm getting shutter speeds in the area of 1/500 or better.
Just like any indoor HS sport, the cycling of the lights will wreak havoc with your white balance. If you shoot in bursts, you'll see what I mean. I'll most of the time set it in-camera either on the cloudy setting or somewhere around the fluorescent setting, tweaking it as needed. I'm not really that concerned though since I know I can process the WB in post processing as all of my shooting is RAW.
Try to get a variety of angles. The usual angles will be hard to get if not on deck, such as the head-on shots of the butterfly and the breaststrokes. But, if you are able to zoom in, side shots of those can look pretty good too. Another popular angle is getting them as they leave the blocks, entering the water. Solo events are hard to isolate your kid, but the relays will allow better isolation after the first leg since they are usually leaving them at different times.
By the end of an 6-8 hour meet, I'm pretty exhausted but it's a lot of fun and the kids love seeing their action shots. Remember to try and acclimate your camera/lens to the humidity since you can have fogging issues when you first go into the natatorium. I don't always have this issue, but it is a very likely possibility. Have fun, stay dry, and good luck!
