* Talking about diaper changing*

So my toddler old goes to preschool. We have tried Itty training but it has been really tough for us. So he wears diapers still. My husband and I noticed after preschool, on the bottom of his penis (the side closer to the testicles are). It was red and irritated. Coming from first time parents who he has only been with us. We have never seen this on him. It hurts him but he isn't scared when we change his diaper. We made an appointment eith the pediatrician and we gave him a bath and just put Vaseline because I worry other stuff might hurt. What are some tips or does this sound concerning? I get worried because I don't know. And also we are going to talk to his preschool tomorrow and ask some questions. I don't want to be rude but I want them to be aware. Any advice on how to bring this up and what questions to ask.