Drink milk. Seriously. And get proper amounts of vitamins and minerals, especially vitamin D.
But you can’t outsmart your genes. There is a range of heights each person may reach based on their genetics. So if your genes say you’ll be about 5’10”, you’ll be roughly 5’10” no matter how well nourished and healthy you are.
This question gets asked from time to time. Basically the only way to affect your height through diet is to be malnourished and end up too small. Otherwise an okay diet and a great diet get you to the same height.
The usual ‘high quality’ as possible stuff. Try and steer them away from too much highly processed stuff like energy drinks, lots of fast food. Lean meat, not too much red meat, protein from other sources too—beans, dairy, fish, eggs; and getting enough fruit, veg, complex carbs.
I’d also make sure they know that smoking/vaping and drinking alcohol aren’t great for you, especially as a teenager, and use of either will impact your brain development and your physical development. I think it’s a great thing to role model stuff like not drinking at every family function, etc.
Tell them that unless they are willing to break their bones and fuse it back together in an expensive time sucking operation just tell them to accept how tall they will grow naturally. There’s just some things that are out of our control that ain’t worth fixing.