When using a food item on a baby mob, which can be both grown and tamed with the same food, the game will prioritize growing. Only when the mob has been fully grown will you be able to tame it. This makes it impossible to tame baby mobs, which is especially problematic in certain game packs, for example Wildlife: Jungle, that contain mobs who can only be tamed as babies.
Thank you for your report!
We're actually already tracking this issue at MCPE-96973, so I will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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