On 35mm film and full frame digital cameras, the "classic" portrait focal lengths fall in the range from 80mm to 135mm. These "short telephoto" are largely preferred for the way they render faces with minimal distortion.
Another thing often wanted in a portrait lens is a large maximum aperture. The primary purpose for that is to be able to blur down a background, to make the subject stand out against it. Of course, you have to tread a fine line and use a lens aperture that will give sufficient depth of field, while still achieving the background blur you want. A large aperture lens may be more desirable in candid shooting situations, where you have less control over the background. A large aperture lens may not be needed for posed portraits, such as in a studio where a backdrop is being used.
Candid situations also may call for the longer focal lengths of the range, allowing the photographer to work from a greater distance and be less intrusive. But you will need more "working space" with longer lenses, too.
Personally I find a 24-70mm lens on full frame "too short" for a lot of portraiture (it's fine on a crop sensor camera, though). Most of the portraits I shoot are candids, too, where I have to deal with all sorts of backgrounds... and to me an f/2.8 aperture just isn't large enough. My "go to" candid portrait lenses on full frame are an 85mm f/1.8 and 135mm f/2. For more formal, posed portraiture I sometimes use a 28-135mm f/3.5-5.6 lens instead. (I also use that lens when I have a lot of hiking to do with my gear, rather than carry a bag full of prime lenses.)
Wedding photographers... who are also primarily portraitists.... tend to rely a lot on a 24-70mm f/2.8 (and 70-200mm f/2.8)... as well as primes with exceptionally large apertures such as 50mm f/1.2 an 85mm f/1.2. However, wedding photography is somewhat unique... shots are often posed, but on location where backgrounds can vary a lot. Wedding photos also tend to be "less tight"... more likely to be at least two people in the shot and, at a minimum, half portraits (head and torso). Often they will even be full length portraits of couples and larger groups. Extra large apertures are used to create a "dreamier" look. There also are some tight candid shots... most likely done with a longer zoom or telephoto prime.
For active kids (and "pet portraits"), a zoom may be necessary.
For "environmental portraits", showing the person in their surroundings for additional context, a shorter focal length such as 50mm (on full frame) or even 35mm or 28mm might be needed. But those need to be used carefully. Shorter focal lengths tend to exaggerate facial features.
Too close with a 50mm lens on full frame will make a person's nose appear large and their ears too small. (50mm is a great "short telephoto/portrait" lens on crop sensor cameras.) Look carefully at the illustration SkyKing shared in an earlier post. The 24mm and 35mm focal lengths significantly distort facial features. 70mm is better... but 85mm and 135mm are even better still.
Depending upon what type of portraits you're shooting and the conditions you're shooting under, you will want to choose different lenses. Maybe that 50mm is perfect for your purposes. Or, maybe not. You might just add an 85mm to your kit and see how that works for you. Or, if you're shooting active portraits you may need a zoom, in which case something in the 24-105 or 28-135mm ranges might be more useful than a 24-70mm. But if you need a large aperture lens due to backgrounds, you'll probably need to work with either 24-70mm or 70-200mm. That might get you to f/2.8.... but if you need larger, you'll be back to using primes instead of zooms.
As a general rule, I don't like to use macro lenses for portraiture. The reason people do so is because macro tend to be short telephotos, much like "ideal" portrait lenses. And it's always nice when a lens can serve dual purposes. But in my opinion macro lenses are simply "too sharp" for portraiture a lot of the time. They also usually have a max aperture of f/2.8 or smaller. An exception I use with crop sensor cameras is the Tamron 60mm f/2.... When macro and portraits are secondary, but possible on a particular shoot, this fairly compact lens takes place of three others to lighten my camera bag (50mm f/1.4, 85mm f/1.8 and 100mm f/2.8 macro). One reason I'll use the Tamron 60mm Macro for portraits is because it has a stop larger aperture than most macro lenses. And it saves me a pound or two to carry, as well as a lot of space in my bag (which has become increasingly important as I've gotten older
). But, it's a crop only lens. So won't be any help to you, using a full frame camera.