we have recently put DS1 (aged 4) in a booster seat for the first time (so DS2 can have his old seat) and he keeps being sick in the car. This has happened on 4 seperate occasions and i think its the booster seat thats causing it. He's now back in his old seat and fine, but DS2 is rapidly outgrowing his 1st stage car seat. anyone have any experience of this?