The Bug
Baby dolphins seem unable to spawn naturally, unlike the other baby mobs added in the same snapshot as baby dolphins (squids and glow squids), making them unobtainable in Survival mode.
Steps to Reproduce
Download this world, extract the folder, and load it in the latest snapshot.
Press the "Kill Squids" button a few times to allow more dolphins to spawn.
Press the "Teleport Dolphins" button. Look closely behind you at each dolphin, noting if it is a baby or an adult.
Once done, press "Kill Dolphins", and repeat steps 2-4 several times, preferably for a few minutes.
Observed Results
Baby dolphins do not spawn naturally.
Expected Results
Baby dolphins would be able to spawn naturally.
Please note that I have tried this for around 45 minutes on two different worlds, with no baby dolphins spawning. I recorded about 10 minutes of footage to attach to this report, but unfortunately, the recording was corrupted, so I do not have any footage of this bug.
I recommend trying this for at least 3-5 minutes before confirming the bug report, just in case. 🙂