One thing I would always recommend for those parents or instructors wanting to teach vocabulary is to make it fun and interesting. YouTube is littered with many learning vocabulary videos but not all of them are effective. The most effective videos are the ones who can hold a students' attention, simplicity and not long. I've found at most, a 5 - 6 min video is best. The video can teach maybe 4 - 5 words at a time.
Also, when teaching vocabulary, another factor you want to look for repetition. A video where they say the same words two or three times with corresponding pictures makes sure the student is learning visually in addition to auditory. Basically word association. Afterwards, I would work build on the the video, work on those words for a couple of days including spelling.
It may seem tedious, but YouTube vids help build a foundation, there will still be work to do outside the vids. For older students, I've found that TV shows and music videos are great for learning vocabulary