I read that it is recommended to show the set of flashcards twice a day: the same cards for 5 days. To share my experience: I usually show LR to my girl in the morning and in the evening. LR scheduled three rounds per session. You can choose word only, word and media, and media only. I choose combination of these in the three rounds:
Morning: word-media(pronounciation of word only); word-media (with audio effects); media only (pronounciation only).
Evening: word-media-word (pronounciation only); word-media (with audio effects); word only (pronounciation only).
Although my daughter finds the audio effects amusing sometimes, e.g. zzz sound from the lizard, da da da from the rabbit, I find my daughter concentrates most at word-media (with only pronounciation of the word and no audio effects during the pictures).
Give your kid a try of the various combinations and find out which one is suitable and gives most attraction!