8 month old in a toddler booster seat

This is the type of car seat my SIL and MIL are putting my 8 month old niece in. Except the one they got is probably 6 years old because it's from my nephews. They seem to have no problem with it and think it's completely normal to have a baby that young in a car seat like this. They've never put her car seat rear facing but this takes the cake. I'm scared of what will happen to her. I just hope my SIL gets pulled over and something happens because I would probably end up in prison if my niece got hurt because of their stupidity.