John: I've updated this bug report's summary and description to refer to all baby mobs. Thank you for the suggestion. I've also attached another screenshot showing the same behavior with sheep. I suspect that Mojang may have done this intentionally to avoid cases where a mob becomes an adult in a confined space (low ceiling) which then causes them to take suffocation damage and die. That should be avoidable if they prevent the mob from growing from a baby to an adult if there is not sufficient headroom. This would also let players create galleries of baby animals that never grow up.
Aaron Graham
John: I've updated this bug report's summary and description to refer to all baby mobs. Thank you for the suggestion. I've also attached another screenshot showing the same behavior with sheep. I suspect that Mojang may have done this intentionally to avoid cases where a mob becomes an adult in a confined space (low ceiling) which then causes them to take suffocation damage and die. That should be avoidable if they prevent the mob from growing from a baby to an adult if there is not sufficient headroom. This would also let players create galleries of baby animals that never grow up.