I assume neonatal.

Infant/Newborn.

@Background Pony #6E84  
someday

@OptimusPrimevil  
So I guess we’re still missing his Mega form.  
Maybe one day…

@ZeroSpawn47  
Hey, not all babies are disgusting– baby spiders are so cute their moms can’t help but carry around like a billion of ’em!  

This image is blocked by your current filter - click here to display it anyway

your current filter.

If this is a baby:  

 
Then WTF is this?  
https://www.google.com/search?q=newborn+infant&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj6-8LJ69_NAhVF0iYKHa7ZDvoQ_AUICCgB&biw=1536&bih=795&dpr=2.5  
(That’s the link to the google image search for “newborn infant.” I didn’t want to actually post a picture of one of those abominations because holy crap they are disgusting. I didn’t want to subject anyone to accidentally seeing one.)

@Background Pony #CCA2  
there’s a pretty good explanati…
 

A phyletically inaccurate suckling reflex?

A younger baby

@Background Pony #CCA2  
Technically pound per pound baby is stronger than an adult.

If Spike is still a baby, then how is he able to hold other babies? heck, he can even hold 3 fillies at once.
 
Babies can’t hold other babies, it’s not scientifically possible.

Hatchling?

@OptimusPrimevil  
I am on the southwest side of the pacific.

@CyanLightning  
terms might be confusing though (depends on what side of the pacific you are)

@OptimusPrimevil  
Love the digimon reference.

 
or if you prefer
 
 
baby II  
Child  
Adult  
Perfect

Extra Baby

@Archonix  

I mean, hasn’t this always been obvious?  
A day-old baby doesn’t look like a 1-2-year old, but they’re both still babies.

Infant

@Background Pony #3CD9  
and/or balut boiled fertilized egg, the one where the duck embryo has visible body parts

Newborn.

@OptimusPrimevil  
A failed abortion?

@Background Pony #3CD9  
nah, that would be spike still in the egg (or if the egg is cracked prematurely)

A fetus

newborn?