Toddler can unbuckle the chest clip of car seat

My daughter will be 2 in February and last night I looked back and saw her chest clip unbuckled and I thought maybe I didn’t click it in all the way so I pulled over and snapped it together. Then started driving and saw her messing with it and unbuckled it herself. How do I get her to stop doing this? I’ve never heard anyone have this problem so I’m clueless!