The Adventures of Flotter

From Memory Alpha, the free Star Trek reference.

The Adventures of Flotter was a series of children's holoprograms set in the Forest of Forever, where colorful characters like Flotter and Trevis (representations of natural elements or forces of nature) helped teach deductive reasoning skills. Some Flotter stories included "Flotter and the Tree Monster", "Flotter and the Perfect Day", "Trevis and the Terribly Twisted Trunk", "Flotter, Trevis, and the Ogre of Fire" and "Flotter Meets the Invincible Invertebrates".

Kathryn Janeway, Harry Kim, B'Elanna Torres and Samantha Wildman enjoyed the Flotter adventures as children, as did Naomi Wildman. The young girl also owned a stuffed Flotter doll. (VOY: "Once Upon a Time") Janeway claims to have flooded the entire forest when she was a child of six. (VOY: "Once Upon a Time", "Lineage")

Since holodecks as we know them are relatively new (as evidenced by comments in TNG: "Encounter at Farpoint"), it seems unlikely that adult crewmembers would have known Flotter in its holographic form. Flotter may have previously existed in other media, but Janeway's flooding of the forest suggests at least some holodeck-like interactivity. Perhaps the Flotter programs Janeway knew were based on a more primitive holodeck predecessor's technology, or were similar to current-day computer games.