Kids should be able to be free thinkers and find their interests with free reign and if it happens to be rap music then so be it. If their parents don't want them to listen to rap songs due to explicit language then they should find the censored versions of the music. It's not hard to learn how and if they're too lazy to figure out how to find the censored versions (just Google "how to censor spotify" or whatever streaming service) then they're not doing enough as parents. Don't give your kids stupid limitations because you're too lazy to actually make them happy while simultaneously enforce your rules as a parent. If your option is to say no to something when there are solutions to make it adhere then you're a crappy parent.
If you want your children to not speak bad words then keep them from it. We have technology to help censor what parents can agree with and what they cannot. Also, I have yet to find any good thing in rap that can help a child develop in society, They have no need for it.
It comes down to the parents on what and why.