I don't see how the art looks "kiddy" to me, tbh. If going by the link, we have a map, a happy tiefling with glowing eyes, a spider-monster holding what looks like a lamp, and a unicorn at night.
The unicorn might have the most "all ages" saccharine flavor given their prominence in stereotypical pre-teen girls' media, but those creatures have been a long-standing monster in fantasy.
This may be a hot take on my part, but the Forgotten Realms always struck me as a bit twee of a setting in comparison to others, as "saccharine" fantasy elements get a lot of coverage even in pre-4e editions. Be it the large emphasis on bardic and nature themes such as with Drizz't's patron deity Mielikki or the Harpers, the preponderance of female spellcasters in leadership positions, Silverymoon being your idyllic beautiful magic city with tree-buildings, the large amount of elven subraces and focus on elves in lore, Magefair festivals that make magic feel less of a forbidden and hidden art and more of something beautiful and wondrous, and so on.