If your daughter told you it happened at school, I would believe her and tend to believe your husband that it was a straddle injury (very common for me when I was that age). The whole concept of sexual abuse doesn't sound likely to me with your daughter then going to a movie and then on a play date? If I were the abused child, I wouldn't be able to do that well enough that the friend's mother wouldn't notice something were wrong? If I were your husband trying to deny something like that, I would start with the initial statement by your daughter and deny that it was anything. It sounds to me, instead, that your husband is just being an insensitive SOB to your concerns.

I'm sorry you didn't get to see her this weekend, I'd call her (do you know her teacher at school?) after school and chat with her and assume there was a slight school accident until I heard anything that definitely countered that.