Wants to get tattoos

Before You Begin
Pause and breathe. Even if this shouldn't be happening... accept that it is and embrace it with composure and calmness.
Calmness is the only way forward because without calm, there is no possibility for receptiveness and connection. Your child won't give to you any more than they see from you.
Never forget that a strong connection is fundamental, as there will be no correction in them if there is no connection with you.
The Core Problem
The appeal and excitement of getting a tattoo is distracting them from the negative impact it could have on their lives.
What Will Make It Worse
Reacting with anger, shaming and/or disappointment will do nothing to bring them in closer to you or put them into a state where they are ready to understand your concerns about the tattoos they want.
What The Child Needs
1. To decide why getting a tattoo is the answer: We get something because there is something missing in our life. Ask them what is missing in their life that a tattoo is the solution to, and explore if there is something that doesn't involve changing their body, or isn't a lifelong commitment, that could be a solution.
2. To know the cost and process for getting and removing a tattoo: Tattoos aren't just a big (and painful) body commitment, they are a big financial commitment. Even more so if you end up getting it removed! Discuss with them if they have a realistic understanding of the cost and discomfort of getting a tattoo, and that both of those are multiplied if they ever want to get rid of it.
3. To consider the social and job consequences of being tattooed: While tattoos are more popular than ever, the ones most intriguing to them are on those who don't have to worry about social acceptance and hire-ability (i.e. celebrities). Your child, on the other hand, might get an unexpected and undeserving cold shoulder by people who don't know them or potential employers. While this is unfair, it is entirely true and something that your child needs understand and anticipate if they want to get a tattoo.
4. To hear stories from those who are older: Have them talk to much older individuals and get their honest thoughts on their tattoos. Whether they love them, hate them, or would have done something different in hindsight, the conversation will be valuable and help your child make a more informed decision.
How To Have The Conversation With Your Child
Find a time when your child is receptive to talking with you, free of distractions.
Let them know that you are taking their interest in getting a tattoo seriously, and for that reason you want to talk about it openly with them.
Share with them that there are a few things you want to hear their thoughts and perspective on.
Use the provided "What The Child Needs" pointers 1-3 to have an engaging two way conversation that is taken seriously but still relaxed enough that it encourages full unguarded honesty and open communication. Avoid letting any frustration or strong disapproval that you may have toward them getting a tattoo come out because your child will quickly put up their walls and any chance of a constructive conversation will disappear.
To show open-mindedness from your side, you could later assist in coordinating the conversations in pointer 4.
Regardless of their age and level of independence from you, keeping them close and helping them make the decision of whether or not to proceed with you, versus in spite of you, will lead to a much better outcome.