Don't beat yourself up, hun Happens to the best of us!! I have had to make a habit of checking the DDs' car seats EVERY time we get in the car now, as DD1 can reach down between them and press the button releasing the seatbelt that holds their carseats in place. I learned my lesson one day when I went around a roundabout and poor DD2 ended up face-down on the back seat, her carseat strapped to her like she was a turtle. I nearly died, I swear, I panicked sooo bad. DD1 still unbuckles the seatbelts despite being told how important it is that she leave them alone, so now it's just one of those things, like checking that the car's in 'P' before turning the key in the ignition, kwim??
Hope you're okay Dianne, please don't feel bad about it! A very simple mistake to make, I'm sure most of us have done it at some stage, and at least you discovered it now and not when something bad happened. *hugs*