My niece came over to play with my kids. My husband was in the shower and the kids were in my room. (The rooms are small and conjoined)

My husband went to open the shower curtain and she was standing there and looked over at him. (He had no idea they were in there) He has no idea what she saw but she was looking at him for a good 4 or 5seconds before he slammed the shower curtain shut and realized.

What should I do or say to her if anything at all?

Obviously this was all accident but I don’t want her to be scared for life. Lol.