Yarn, two colors (standard worsted-weight acrylic which usually costs under $5 will be fine -- if the learner is new to crochet, light or bright colors are better than dark colors)
Scissors for yarn (nail clippers will work if the parent wants the learner to be extra safe)
Crochet hook compatible with the yarn (if using the recommended yarn, about a G or H hook -- also under $5)
Stitch markers (if official ones are not available, learners can use paper clips or a different color of yarn) (under $2)
If anyone in the family is or is likely to be a crochet enthusiast, a kit with many sizes of ergonomic hooks and other tools like needles and stitch markers, like this one https://www.amazon.com/WooCrafts-Large-Eye-Ergonomic-Arthritic-Hands-Best/dp/B06XHHJ1TV/ , is worth considering. The larger grip can also be easier for beginners, just like little kids using bigger crayons.
Storage for supplies and completed projects
Optional: yarn needle for tucking in ends (comes in most kits, or available separately, but if you haven't got one, you can use the hook)

Learners will need to use age-appropriate functional sharp objects (scissors and possibly yarn needles) to cut yarn and tuck in ends. If desired for safety purposes, nail clippers can be used instead of scissors to cut yarn, and the crochet hook can be used to tuck in ends.