I always advise people who are 'new' to music, that guitar, uke, or violin etc, are difficult for young children, as they have to put in a lot of effort and, in the early stages, don't get very much musical satisfaction.
Much better - easier and more satisfying - I always think, is a good modern Keyboard, with full-size keys - at least 61 of them, or if you can afford it, 76.
A Keyboard will have around 500 different sounds, including several 'guitar' voices of different sorts - acoustic guitar, electric guitar, rock guitar, jazz guitar and more. There will also be 'automatic' accompaniments in numerous styles, to enhance the lead, solo voice, and various 'learning' modes to help the beginner to get started with playing, and learning to read music.
If most of the appeal of guitar is its appearance, and the image of solo guitarists on TV, then Keyboard may not be the answer, but if there is an interest to learn about sounds, music, and different styles, a Keyboard can produce satisfying music much more quickly than a traditional stringed instrument.