Brought back memories of pulling onto my driveway 27 years ago, hearing the rear door slam and watching in horror as a just visible little tuft of hair went past the passenger door window toward the gate! My 3 year old son had undone his car seat and got out. He also climbed up a chimney. Climbed out of his cot in the middle of the night, went downstairs in the dark (must have been all those carrots), got all his toys out, went back upstairs climbed back in and went to sleep. He survived! He also emptied his sandpit through the bathroom window and the loo had a large pile of sand on it. I could go on. Bless him. Depending on your granddaughter's size and weight you can keep them in a rear facing seat until 3 I hear. So if she did slip the straps, would be safer in a collision. Or, invest in a seat mounted DVD player. Put her favourite film on before setting off and say she can only watch if she stays put. If she's interested in something and not bored, she may well sit quietly and watch Little Mermaid or something. If all else fails, no journeys without an adult I guess, although not always practical I'm sure. Little rascals aren't they.