I don't think you do get it, do you understand statistics? Yes, paedophiles are statistically far more likely to be men, but true paedophiles are a tiny, tiny minority of the male population. 99.5% (I'm guessing) do not have a sexual interest in children. And I expect only a very small proportion of that 0.5% have a sexual interest in their own children (in fact they're probably highly protective of their own children - judging everyone else by their own standards etc). I wouldn't like to speculate what percentage of women are paedophiles, but it's certainly going to be even smaller. But male or female, the risks in these circumstances are miniscule.
I also think there's unlikely to be any significant correlation between a man who abuses his adult partner and paedophilia. As abhorent as they both are, they're quite different things. If anything, most paedophiles are generally quite submissive and timid around other adults, instead they take their control out over minors.
As for the initial question, I don't see any issue with a man bathing with his young children (unless a known paedophile obviously), not any different to a mother doing the same. One of my DCs used to love jumping in the bath with my dp, but they grew out of it by about age 7 and started showering instead.
And what about a man bathing his child without getting in with them? Does anyone take issue with that? No they don't. Yet a man who's going to sexually abuse his children is just as likely to do it over the side of the bath as they are sharing it.