Regarding R-day and the weeks that follow, parents of new cadets should be advised in general to stay away. I don't think there is a problem just attending the concert, but for sure beyond that you should just stay home. First, you don't want your new Cadet seeing you or thinking you might be there. Second, WP will warn you not to be there and will do what it can to chase you out. But mostly, for yourself you shouldn't be there.
Honestly, that seven weeks between R-day and A-day was very hard. My son and I have been best buddies and spent a ton of time together. When he went to WP that was very difficult. It is hard core, because you don't really hear from them at all, beyond a couple phone calls and in our case a few letters which don't arive until about 2 1/2 weeks after he sent them. We drove home to Michigan immediately after the R-Day oath, and didn't go back till A-Day. Staying for the concert would have been like a smoker who is trying to quit, then hanging out at a bar with a group of smokers the day after you quit.
Last year's concert was supposed to be streamed live, but they had technical problems, but I bet this year's concert will be. The Thayer did a video of all the cadets marching in. It was great, and you get a better look at your kid with that then you would if you were there.
Just my two cents.