This guide explains what Upsies! API-compatible items and where to find them.
Upsies! API compatible items are furniture and accessories built by Second Life creators that connect directly to a baby’s Upsies!. They add extra functionality to roleplay, like letting a parent or caregiver adjust, sit, or play with their child using the same permissions already set up in the child’s Upsies!.
Compatible items use the parent and caregiver permissions a child has already set in their Upsies!, so there is no extra setup needed for the caregiver.
Creators who build Upsies! API compatible items display the Upsies! API-compatible logo on their listings and in their stores. Look for this logo when shopping to know an item will work with Upsies!.

Starries keeps an official page listing Upsies! API compatible items and the creators who make them:

For questions about a specific compatible item or about becoming an API-compatible creator, contact Starries directly. For questions about how MoonBots bots work with Upsies!, MoonBots support is happy to help.