Colt/Filly should imply Foal.

colt / filly > foal
 
Maybe? idk, just feels right, but maybe no one wants this.

@LightningBolt
 
Sounds good, i guess.

Colt and filly are roughly equivalent to boy and girl, while foal is more like baby.

@Archonix
 
Except that we already have the “baby pony” tag for that.

@Archonix  
Sounds about right.
 
@Mildgyth  
I thought ‘baby pony’ was more for these young foals like >>1329143

Foal the equivalent of child, baby is the equivalent of…baby.
 
Tho if I tried to follow this by G1 toyline logic, ‘baby’ is closer to child, newborn is baby, and teeny tiny is newborn.

@Archonix  
That doesn’t explain the “foalcon” tag then. Foal is definitely the term used for a young male/female, at least in this fandom. Foal in the real world applies to both a baby horse and a young/adolescent horse (hence terms like “foaling” or “foaled” aka the process of giving birth to a foal).
 
Anyway, I like OP’s idea.