@SimGuruIcarus -
I uploaded 2 files for your testing pleasure 🙂 Both show that some of the the sims in the family display toddler traits in the relationship panels of others, and some do not. Both files are the same family (a legacy household that I'm playing), with a toddler in the first file, who aged up to child in the second file.
How they aged up does not seem important, and when they aged up (before or after GF patch) does not seem to be the issue. It appears that if the sim knew the sim when they were a toddler and learned the toddler trait, they will retain the toddler trait in the relationship panel. There is a case where a younger sister is showing the toddler trait for an older sister, but it's important to note that they were both toddlers together at one point. (Gabriella shows older sister Georgia's toddler trait Inquisitive in her relationship panel.)
A breakdown of the relationships and traits:
In both files:
Grace - aged before GF; no party or cake, game aged her. Toddler trait: Wild
Gretchen - aged before GF; had party but game aged her up before blowing out the candles. Toddler Trait: Independent
Georgia - aged before GF; no party or cake, game aged her. Toddler Trait: Inquisitive
Gabriella - aged before GF; had party, aged via cake. Toddler trait: Clingy
Lane (twin) - aged after GF; no party, aged via cake. Toddler trait: Angelic
Wyatt (twin) - aged after GF; no party, aged via cake. Toddler trait: Charmer
Martin - aged after GF; no party or cake, game aged him (still a toddler in first file). Toddler trait: Angelic
In ToddlerTraits 1 file:
Grace (Adult traits: Good, Romantic, Hot Headed) - Good friends or better with all family members; shows all adult traits in all relationship panels
Gretchen (Adult traits: Goofball, Self-Assured, Hates Children) - Friend or better with all family members; shows all adult traits in all relationship panels
Georgia (Adult traits: Slob, Loner, Hot Headed) - Grace & Gretchen:Good Friends (Older Sisters):Shows Inquisitive/Loner/Hot Headed; Gabriella:Good Friends (Younger Sister):Shows Inquisitive/Loner/Hot Headed); All other family members are Friend or better; shows all adult traits
Gabriella (Adult traits: Creative, Neat, Jealous) - Grace, Gretchen & Georgia:Good Friends (Older Sisters); Shows Neat/Creative/Clingy; All others (Younger brothers & brother-in-law met after aged up) are Friend or better and show all adult traits
Lane (Teen traits: Cheerful, Foodie) - Martin:Friend (Younger brother) shows correct Teen traits; Everyone else are Friends or better and show Cheerful/Angelic
Wyatt (Teen traits: Goofball, Childish) - Martin:Friend (Younger brother) shows correct Teen traits; Everyone else are Friends or better and show Childish/Charmer
Martin (Toddler trait: Angelic) - All are Friends or better and show the correct Toddler trait
In ToddlerTraits 2 file:
All of the traits are the same as in ToddlerTraits 1, except in this file Martin aged up from toddler to child.
Martin (Child trait: Self-Assured) - All are Friends or better; All show the toddler trait Angelic
I've included the above information in a text file along with the 2 save files here. I have only Base Game, Romantic Garden, and freebies Holiday pack & Grim's guitar. No mods or cc - never used. Hope this is useful; if you want anything else, let me know. I believe I have some save files from before the adults were aged up, if you need.