Bad Business is among the millions of user-created games on Roblox, the kids’ entertainment set to go public on Wednesday after being valued at $29.5 billion in January.

Ethan Gawronski was about 10 years old when he discovered Roblox. He dove into its games, mostly to socialize with other kids. Now, at age 20, Gawronski has his own Roblox game that he works on full ...