a child sim in the family keeps randomising

hello!! ive been building up a family household but after sending one of the child sims to play in the park, when i returned home, the other child in the family had their appearance entirely randomised. im pretty sure the features were the same, but skin tone, hair, clothing etc. got randomised. nothing else was affected, just the appearance of the 2nd kid. i closed the game without saving and opened the game back up at the latest save, where the issue fixed itself! but when i travelled to a different lot with a sim and returned, the same issue happened. i have no idea what could be causing this, and i want to be able to leave the home lot !! 

i play with mods & cc and i suspect it to be the cause of the issue, but it didn't affect anything before the family had children. what does one do about a situation like this ?