My daughter will be 5 in December. She's currently FF in a TrueFit and a Radian (depending on which car she's in). She's about 43" tall and 38lbs, so she has MILES to go before she outgrows either seat. We're definitely planning on using both of them to the max, and are pleased beyond punch that they still are fitting her so well and have room to grow still. These were both used for her from *birth* (7 lbs), so they were definitely well worth the investment!!
The law for booster seat use in our province is a minimum of 40lbs. She's almost there -- and like I said, we are NOT planning to switch her to a booster the day she hits 40lbs, but will ride out the 5-pt harnesses as long as we can.
BUT -- it would be nice if we could just use a simple booster when we're travelling in someone ELSE's car. Don't get me wrong, the TrueFit especially is remarkably easy to install into just about any car we've tried so far, it's definitely my favourite car seat EVER. But, it's still an annoyance to have to do it, and it's big to lug around, and it's harder to fit more kids in the back, etc etc.
I'm quite well-versed in the real safety rules (as opposed to the laws) when it comes to infants and extended RF and all that, but I'm new to THIS part of the transition. :) I do know that just because the law allows it, doesn't necessarily mean it's a good idea.
So I'm asking the wise folks here -- would YOU allow a 40lb 5yo to ride in a booster seat *occasionally*, or would you wait until they were bigger and continue to deal with swapping out the car seats? If you would wait, what would your minimum age/size be and what are the physiological reasons for it?
Thanks for any advice!