WHY? WHY? WHY ?

cas.fulleditmode and change their weight in CAS, if you do not want to play them to loose their weight. Very simple and fast :)

I used to have the opposite problem before I began defining "fit" and "fat" limits in MCCC. Mine used to age up into unnaturally thin teenagers every single time, no matter what in-game potential solutions I tried. Many newly-aged-up teens should be thin, yes, but not so much that if they turn sideways they virtually disappear. :lol:

I have this issue as well. I don’t think my sims eat unhealthy.

I used to have this happen in my game all the time too! But the problem went away after a while for me, so I'm not sure if it was a bug or if it just sort of happened more often in the past. Now the kids in my game usually grow up to have similar body shapes to their parents unless I have them eat a lot or something. I wonder what causes this?

The secret is actually very simple - eating more than you need to contributes to sim getting fat. In game it is represented by their hunger meter. Once this meter is full, Sim will start gaining weight form any food they eat. Consider food a simple sustenance and eat only as much as you need and this probelm alleviates itself VERY noticeably. This is also why vampires don't really get fat - they don't drink more than they need to.

My first couple of Sims 4 games had this issue but not more recently.
I don't use mods. I use standard aging and don't age up babies early.
Two things I changed:
1. I have been having my characters exercise more often at all ages, like a very active character will go jogging or use workout equipment once or twice a day, a lazy one will exercise once a week or less, and the others in between. Anyone feeling energized will do a few situps or something. Characters are allowed to play with soccer ball, basketball, pool when they feel like it. Kids get to play on monkey bars or jungle gym a few times a week. I notice also that townies are more in shape now than in my first couple of games, too. I've heard that townies tend to follow the habits of your played sims to some extent, maybe others can confirm. I'm currently farther into a legacy than I have been before (gen 4 is teens) and have yet to encounter the plague of "pear-shaped townies" that people describe. The townies are a nice variety of body shapes and sizes.
2. My toddlers eat normal food and harvestables now, no more quick meals. That happened mostly because I got tired of high chairs, but these toddlers do seem to grow up in better shape. I wonder if all those quick meals maybe added up to being overweight? Quick meals can have that effect on older sims.

Or it could just be that this was adjusted in a patch somewhere along the line. Is your game fully updated?

Mine are always average. I wish I would get a few overweight teens or very thin teens just so I can work on getting them to a healthy size.

Same is happening with mine. Every baby ages up into a toddler with the weight bar all the way up

I haven't had chubby teens for a while on my saves, even if I've had lots of kids aged up into teens lately. I've had a bit of an opposite thing happening, especially a lot of the teen boys are very skinny and I often end up making them use the gym machine to make their string like arms and legs match to the rest of their body.
I'd actually like to have more variety on my teens, I'd be happy to have some of them bigger size than others. Whenever a child ages up into a chubby teen it's such a rare thing that I end up getting very attached to them and protecting them at all costs. :)

big mood

though for me they are like max fatness already as toddlers and kids

i have started giving them the insta lean drink you can get with aspiration points cause i got rather annoyed at my sims spawn always ending up fat

i recall in my first sims 4 save though i had opposite problem of sims turning out being literal stick figures everytime and then i had to always give them sparta training and lots of overeating when they reach teen so they stop looking like they dont know what bread is

also idk what up but yesterday i added curious brothers in my game and their hunger goes down like crazy fast

i mean one of them has the alien baby but other brothers hunger also goes down crazy fast as if they are pregnant too and well if not weird at least very curious indeed

its literally one brother at fridge every time of the day cause their hunger went on red out of nowhere

don't even have any mods so idk what it about