For one, it is making no pretense to be bridging the two digital realms.

Users of Douyin are entirely walled off from users of TikTok and vice versa; the better to manage the material that people in China can see. Beijing’s tightening controls have made these decidedly un-fun times to be in the business of fun.

Video game companies, celebrity gossip bloggers and live-streaming stars have all been through the wringer recently as the government works harder to stamp out cultural content that it deems unhealthy or unwholesome. The crackdown has not spared Bytedance — the authorities ordered the company’s joke-sharing app offline in April this year.

The company has also crossed borders with relative ease by focusing on light, affirming fare, and on attracting young — very young — users. But the Chinese Communist Party is not alone in having discovered a sordid side to Bytedance’s platforms.

Both before the company bought Musical.ly and since, horrified parents and others have reported finding adolescent users showing off suggestive dance moves on the app, mouthing lyrics about rough sex and worse. Police in Britain have investigated reports of adults propositioning children through Musical.ly.

Bytedance added new privacy settings and parental controls to TikTok in June. But if the company, which declined to comment for this article, cannot expand its ability to manage such issues at the same rapid clip at which it is drawing new users, its products could become the bane of many more parents and governments in many more countries.

Their children might not care.

Kang Sae-eun, 14, an eighth grader in Seoul, loves watching other young South Koreans on TikTok. There’s the girl who makes crazy faces, and the excellent dancer. There’s the cool girl with short hair — real “girl crush” material, she said.

They are funny and uninhibited, Sae-eun said. And best of all, they are regular kids like her.

“It is much harder for young people like elementary school students to become famous on the better-known platforms, like YouTube, Facebook or Instagram, all of which I also use,” she said.