Hi, so my middle child is 4, 41lbs and 42", in a Britax Frontier CT. He's also a hard-headed, pain in the....carseat, who, once he finds a button, will not stop pressing it. We were doing 70km/h two days ago, when he proudly said "look! my carseat!" He'd loosened it to the point where his arms were fully extended forward, with the chest clip in his hands. So we pulled over, fixed it and went home. I had him show me how he did it: slipped his hand into the outer crotch buckle slot in the cover, worked hella hard to reach for the harness adjuster release, pumped it a few times to slightly loosen, then held it down and leaned forward until completely loose. So I decide to change out his seat to a Boulevard CT I had waiting for his younger brother to turn FF. As I'm adjusting the harness height to him, and I put him in, nice and snug, he says "Ha, I can do this one too I bet" and reaches down, finger into the hole, struggles at first, then depresses the button and leans forward. So back to the Frontier. We sewed the outer crotch strap slot shut, reinstalled it and were done. Today we were driving and he did it again! I have him show me (he's proud of his defiance, so he does) - struggles hard to pull and yank on the cover, gets it up, sticks his hand through the harness adjuster slot and loosens the harness. I can't sew it shut because I might need to loosen it in a hurry someday. The kicker is that we have one in our other car for him too, and we hit the highway twice a week in that tiny hatchback, doing high speeds amongst mostly much bigger vehicles. I've given him hell, I showed him some crash test videos, I showed him some not-too-gory pics of kids in neckbraces with some minor facial lacerations (telling him they'd loosened their harnesses). Nothing. He will do this over and over. He's not a reward/punishment guy. His biggest carrot is having the power to make mommy pull over. I'm not too hip on buying him another extended RF seat in hopes he can't reach it for lying back (diono, 45lbs) 'cause it's expensive as hell. I'm happy (ish) to buy for both cars, a different FF (not too expensive) seat that has the harness adjuster really far down the front. Any ideas? What do I do? He's going to need to be in a 5 point harness until he's 25 years old and has grown a full pre-fontal cortex!