I have 2 booster seats with backs for my 2, there is no room to fit another booster in the middle at the back, but there is a seat belt (shoulder one not lap belt). There will be no one in the front passenger seat, but it has an airbag.
So where would you put the visiting DC for 2 20 minute journeys? in the middle back? in my oldest child's booster seat ?(and my child in middle back?) in the front in borrowed booster seat?
This is an unexpected lift I have to do today as a favour - can get a spare booster seat but can't speak to Mum to find out where she would like him to sit.
If you can get a borrowed booster then I'd put own child in front in booster and other child in back. If you can't get a booster then biggest child in middle back with just seatbelt, other 2 in boosters in back
Sometimes these situations are just plain unavoidable.
I always put the visiting child in the 'safest' seat, so in your situation that would be in the back and then I put my DS in the front, usually without a booster seat though as I only have one. Car does have airbag, but chances are that everything will be fine.
Or you could put your DS in the middle back?
I must check the height limit for not having a booster seat though as DS is quite tall and he must be close to it.
i woul definitely have him on a booster if you can. push the front seast right back. AFAIK this is what is recommended for children on boosters in front seats with airbags. i think it is rear facing seats that cannot go in teh front.