No. There are quite a few problems with this.
1. Dwarves dont always use interactions, so assuming the mother will use it on a child is not guaranteed.
This, I didn't know; I was going off of the wording in
http://dwarffortresswiki.org/index.php/DF2014:Syndrome#Spreading_diseases for a creature using an interaction to add a syndrome on line of sight.
[/quote]
It used to be true that a unit would use a LOS interaction almost immediately upon it becoming available for use.
3. There is no loop to go back if all possibilities fail on a transform.
If #1 wasn't an issue, wouldn't doing something like
[SYNDROME]
[SYN_NAME:placeholder]
[SYN_AFFECTED_CLASS:GENERAL_POISON]
[CE_BODY_TRANSFORMATION:PROB:50:START:0]
[CE:CREATURE:DWARF:MALE]
[CE_BODY_TRANSFORMATION:PROB:50:START:0]
[CE:CREATURE:DWARF:FEMALE]
[CE_BODY_TRANSFORMATION:PROB:100:START:0:END:1]
[CE:CREATURE:DWARF:BABY]
work? (With BABY being a new popratio:100 caste obviously)
If you were going to do this I would suggest just having the interaction only able to target the BABY caste, or give the BABY caste a specific creature class and only let the syndrome change that creature class (although I would go with the first and use IT_AFFECTED_CREATURE)
One thing to note, unless it has changed recently, setting a pop ratio to 0 actually sets it to 1. I remember generating games with a pop ratio 10000 caste and a pop ratio 0 caste and still (very rarely) having the pop ratio caste appear in legends and show up at the fort as migrants (although at the moment I can't remember if one was ever given birth to in my fortress).
Also, it's very likely that most of the population in legends will be the BABY caste as I don't believe the transformation interactions would work correctly during worldgen, also since the vast majority (if not all) will start as the BABY caste there won't be anyone available to do the interaction