Many children show signs of fear in the bathtub. Actually it is a good thing, as water can be so dangerous for young children, so you don’t ever want your son to take it too casually. I think I’d go at your problem by showing him how the shower mechanism works. I don’t know the details of your tub-shower system, but I am guessing that you have to do something with the faucet mechanism to turn the shower on (lift a knob or turn a lever in a certain way). After you draw the water for his bath and while he stands beside you outside the tub, demonstrate the way the shower works. Then make a big deal of fixing the knob or lever so that the shower can’t come on accidentally. Use tape to hold it to the wall in the “tub only” position and say, “There’s no way that shower can come on while we’ve got it taped.”
Until his fear subsides, you might just want to wash him up a bit each night with a washcloth and not put him in the tub. Skipping a bath now and then isn’t going to make him sick or interfere with habits of personal hygiene you are trying to encourage. Then finally, buy a really neat new bathtub toy that he will want to play with. Make it clear that the toy is only for when he is in the tub.
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