This morning my 3.5 year old figured out how to loosen the straps on her car seat. I talked to her about how important it is to keep the straps tight, and asked her not to play with them again. But, I'm nervous that she will do it again, and that next time I'll be driving and unable to re-tighten them (this morning I was putting her sister in the car when she did it). Has anyone else experienced this? Any suggestions on how to prevent her from loosening the straps?