When the cat (not ocelot) has a negative age indicator (age), if you sneak, you get damage from suffocation. This doesn't happen with ocelots-kittens, only with cats. Version 1.12.2, the latest version of the mod. The same thing happens with the "Not Enough Pets" mod when you are a kitten. But this also happens in vanilla minecraft, just with Metamorph.
As a result, you die quickly in non-peaceful mode(

I also checked rabbits and wolves -- it doesn't happen to their children.

I bet the eye level when you are a baby cat and are sneaking is lower than ground level causing this suffocation damage.