What seat in front for tall 4.5 year old?

[pinkypig]

I am travelling in a hire car to see a friend and have 3 children currently in car seats. As hubby is not travelling I was hoping to get a small booster cushion for the eldest and put him in the front seat. Is this legal? Is it dangerous? Do I need to turn off the air bag or because he would only be in a booster cushion (and not a full size car seat) would the air bag be ok to leave on?

Alternatively I can try to squeeze him in a booster cushion in middle of back seat but not sure it will fit in a Prius between 2 full size car seats...

Thanks

legally you can put him in the front on a booster,with the airbag on,but personally i wouldnt.
i would get him a highbacked booster with side impact protection and turn the airbag off.

thank you for the replies

I would 2nd sazms sugestion of getting a highbacked booster. Halfords have the britax adventure for £30 at the moment.
If putting him up front i would switch airbag off if u can. If this is not possible then move the seat as far back form the dash as possible, put your smallest dc behind him if there not much leg room left!!