Where do you get the value from JSON and set the scale to the body? Is it in "On Start of layout" event? Then change the scale of baby arms/legs in the same event.
You are either doing this before the hierarchy is created, or on every tick, it's not clear from your screenshots. There is no point in updating the scale on every tick.
Also, like I said, use "Pick children" instead of picking by Member variable. It's possible that the variable is not yet set or set incorrectly, that's why it's not working.
Try "Body pick children" and if this doesn't work, please post a screenshot of the event sheet showing all relevant events.