We went to a neighbourhood child's birthday party and no JW noticed or said anything (even though an elder's family lives only a few houses up from them). The party was indoors, so it wasn't like we were on the front lawn for everyone to see.
We decided to drive to the home (even though it is just a few houses up from us) because the JWs were out in service that morning on our street...and we didn't want to be seen walking down the street with a Princess party gift bag.
An elder also knocked on our door as we were just about to leave. I didn't view it as a "sign" that I shouldn't go or anything. It is what it is.
Have fun if you decide to go! I'm not sure how likely it will be for anyone to find out you went or not. I'm at the point now where I don't care if I'm outed, but I definitely understand the fear and have been there.