While current statistics on sexual abuse in nursery settings is unavailable (the best data I know of is an old study from the 70s), general statistics show that child sexual abuse is perpetrated by males 96% of the time. It is also generally more severe when committed by males, and more likely to involve penetration and sadism.
So, males are approximately 32 times more likely to sexually abuse children than females despite the fact that they spend much less time in contact with children, so have less opportunity to offend. If they spent an equal amount of time in contact with children as male nursery workers, that number might be higher.
Add into that the fact that 4% of the male population is sexually attracted to under-10s, and would abuse them if they thought they could get away with it, and that men who are sexually attracted to children are nearly 3 times more likely to work with them than other men...
You're looking at a situation where paedophiles see nurseries as perfect hunting grounds, and actively coach each other online on how to look like the perfect, harmless, wholesome male role model. Decent men are less likely to want to work in nurseries, and those who do want to are discouraged due to low pay, and yes, stigma. But paedophiles are not discouraged - they're highly motivated, and as everyone should know, can be excellent at appearing likeable, or even pillars of the community, since they groom parents just as much as their victims.
So you end up with nurseries where: paedophiles are actively trying to infiltrate them, because men who are sexually attracted to children are three times more likely to want to work with them, and men in general are 32 times more likely to sexually abuse children, while in addition, one offender can have hundreds of victims.
By adding male nursery workers, the risk of sexual abuse skyrockets.
I'm not sure why people would want to put their child into an environment where the risk of sexual abuse is deliberately and unnecessarily elevated. What needs to happen is that males need to be banned from working in nurseries, females need to be paid higher wages to make the job more attractive, and safeguarding needs to be stepped up.