Nice guy, worked in childrens' youth groups, babysat my little brother (15 yrs younger than me).
I would consider those pretty big red flags. Very few young men voluntarily offer to babysit and work in youth groups. Child abusers tend to look for opportunities to be in the proximity of children in a respectable position so they can earn the trust of parents and kids.
I actually think you need to look out for men who appear "too good to be true". The ones who seem to be bending over backwards to appear like the perfect father, husband, friend, churchgoer from the outside. They seem to be going to extreme lengths to avoid being judged by other people. They talk with constant name dropping or make sure people know about the good things they've done. This is also common with grandiose narcissists, so it doesn't necessarily mean CSA, but you still don't want to get too close to narcs.
Another subtle red flag is the behaviour of their children. Some children have a "tired aura" about them. They rarely smile in photos. They may not be extroverts but they are very social and tend to cling to friends and clubs because it means they're out of the house. They have behavioural issues in school that aren't directly related to diagnosed ND or SEN. Listen to your child when they tell you stories of what happened in class. Then may talk about certain friends who repeatedly get in trouble or act up.
Patchwork families are also statistically at much higher risk for abuse. The most common type of CSA is perpetrated by unrelated male family members living in the same house. So if there is a stepfather or older stepbrothers in the picture, then the baseline risk is significantly higher. This is obviously NOT saying that all stepfathers are abusers, but the statistics are massively raised. Another red flag would be single mums who are actively dating. There was a MN thread a few days ago from an OP who was annoyed she wasn't told about a random boyfriend staying over during the same night her daughter had a sleepover.
I'm almost certain that one of my best friends growing up was being abused by her father. There were so many red flags looking back as an adult. He was a quiet guy who always kept to himself, especially if her friends were around. It was almost like he didn't want to risk any of her friends picking up on weird vibes or having his daughter mention something. She was a very sweet only child who went off the rails during puberty (smoking, drinking, partying) and moved out of the house at 18 and never came back. The whole house always had a "dark" energy to it. Even though both parents remained married, it didn't feel like a happy place. It's possibly her mum knew what was going on but turned a blind eye.