I am convinced that for children who don't like showers, it's because they don't like it on their face.
I heard too many stories from friends about their child hating showers. Many of them also say their children don't like swimming at the beach. Water at bathtime is fine, but when it's in a bit more of a chaotic situation, their children are not happy.
I live in Hawaii, and I have always grown up around the beach, so being afraid of the beach is kind of a problem. So I decided that I would teach my daughter to not fear showers or the beach by doing something very simple during bath times.
As soon as she was too big for sink bathing, I started bathing her in the bathtub with me. We had a shower head that allowed me to gently wash her down while I held her on my lap. At every bath time, I would intentionally spray just a bit of water on her hair at first. Just a small amount. Oh, she didn't like it at first but eventually we got to the point where I was able to spray just a bit on her face as well. Not very much water, mind you. Almost an instant, gentle spray of water. Not a face full or anything. Just enough to get her used to water on her face. That was the secret -- getting her used to water splashing on her face.
I did this over and over again, every time I bathed her, which was every day. Eventually, she didn't fuss about it. Eventually, she just got used to it.
By the age of 4, she was able to wash her own hair in the shower. I mean, put her face under the shower head, eyes closed with shampoo. Washed her own hair and everying. She's awesome at it. Friends wanted to know how she was able to do that.
She's now 6 and isn't scared of waves at the beach (even choppy waves like Waimanalo Beach). She even wants me to take her into the water, even though she actually doesn't know how to swim yet. The splashing of water does not phase her.
For you new parents out there, give this technique a try when they're young. I am willing to bet that your child will not have a problem with shower time using this technique.