Translation:The children in the garden are cheerful.
Vidam ends in -am but is NOT a possessive. Just like zokni is not a verb. I suspect it is to shake people out of thinking there is always a link with suffixes.
Duolingo lessons often introduce not only new grammar but also new vocabulary. Perhaps this sentence contains a new word -- is kert from the possessive lesson, perhaps, to teach things like "his garden"? And then this is a sentence to strengthen the new word as well.
This sentence introduces vidám - kert is from the much earlier Household lesson.
Maybe later their cheerfulness will be limitless: "Vidámságuk határtalan".
Or maybe it is just Duo's way of checking if you are still paying attention. :) It happens everywhere.
Are there other English words that could be used to translate vidám, besides "cheerful?" Nothing wrong with the word, but from previous exposures to the word, I had the feeling it also meant things like lively, vivacious, etc.
I guess probably depending on context happy, merry, jolly, blithe and all your suggestions should fit.
I assume while pretty, beautiful and gorgeous are rankable, these might be even more blurry.
boldog for happy or élénk for lively are possibly better, but like in English there seem to be a lot of synonyms, which probably all have slightly different meanings. https://szinonimaszotar.hu/keres/vidám
Hmm. I came here just now to ask this question, and I see that I've already done so. Would "joyful" also be a good translation? "Playful?" I'm trying to think of a good word to apply to kids playing in the yard (aka garden).
No, I'm pretty sure it can't. For "cheerful kids" you'd need the adjective to come before the noun. And the adjective would be in singular form, because adjectives before a noun don't have to agree in number. Also, if you're saying that the children are in the garden, then you'd need "vannak" in the sentence, because you're talking about where they are.
A vidám gyerekek a kertben vannak" - The cheerful children are in the garden.