If DD2 is asleep in the back (12kgs) and DD1 (17kgs) is in the front and gets out I just hold onto the pram the whole time and put my backpack nappy bag in the front, I haven't had a problem with that.

I do have DD2 in the front as well and DD1 in the back and the pram doesn't feel like its going to tip, it means DD1 can get out whenever she wants.

Cheers,

Beck