Welcome to our forum.
maybe it is wrong but my 2 year old loves the tub. Last night the tub was 104 and he absolutely loved it. He goes in about 3 to 4 nights a week with me. we limit his tub to 20 min only and then he gets out. As soon as he gets out, we give him a big drink of juice and send him off to bed.The doctor said no less than two and limit to about 20 min.
It would be interesting to take his temperature right before he gets in and again right when he gets out.
For what it is worth, they also said drinking alcohol in a hot tub is not recommended.