First worry should definitely be people who want to rape your kids.
Second should be kids being pressured into sending private pictures of themselves, which is really bad, but still not as bad as #1.
Third should be kids viewing hardcore porn, but by 14 you can already assume they've seen all the worst shit. Even before internet video I remember seeing VHS tapes with girls getting rammed by tree-trunk sized objects while I played D&D with my mostly male friends, and that was probably like age 15.
Fourth worry should be whether your kid is stupid.
Everything else seems easily recoverable.
Modern rap music? It's all mumble/auto-tune bullshit, the only reason to worry about it is if your kid actually likes it, see #4.
Your kids' eyes are only as safe as the most permissive parent of any kid they interact with. I remember being put in 10th grade Biology when I was 13-14 and the teacher made me sit at a lab table with these two guys who were absolutely disgusting edgelord perverts who simultaneously thought I was cool because I was really into computers and Usenet/BBSes like they were, but would try to force me to look at really disgusting porno mags and constantly talked about wanting to rape me and murder my parents and would put dissected animal eyeballs/body parts in the hood of my hoodie.