Depends how you are raising your kids. Think about yourself at 14. What were you watching and exposed to? Would you want to see a movie like Deadpool? What are you kids currently into? How do you think they would feel hearing and seeing things like violence and some mild sexual stuff?
I dont have kids, but if I had 14 year old boys I would for sure take them to see Deadpool. I think of myself at 14 and I had already gotten my hands on a few playboys mags and was watching cinemax softcore stuff whenever I could. I knew about girls, hadnt dated one yet but it wasnt from lack of trying. Same with my friends. So sexual stuff was nothing new to us, we had classes in school, knew what condoms were, about stds, all the basics, and girls were starting to come to school with less and less clothes on.
As for violence, I grew up watching wrestling and football since I was in diapers. Around age 14 I was crazy about the matrix which had just come out and which has tons of violence. I had seen classics like Rambo or Rocky and Alien or Freddy and those types of violent and horror movies. I was big into rap music like eminem at the time and others who use tons of sexual and violent language. So at 14 I was already exposed and used to a bit more mature themes in tv/movies/music like sex, violence, language, drugs, etc.
If my dad wanted to take me to deadpool at 14 I think I would be ok watching it and would be crazy excited and think my dad is the coolest dad in the world. So if your kids are kinda into general pop culture stuff, you know tv, music, movies, clothes, the way they speak and dont live to sheltered of a life they should be mature enough to watch the deadpool movie.