I've got 3 small DC and I don't drive. We mostly walk, but occasionally need to use taxis. I have lightweight booster-seat, but carrying three of those plus whatever else we need plus holding the hand of the youngest is hard work because they're such an awkward shape.
I have been looking at the Trunki Boostapak It is a booster-seat in a backpack. I thought that the 6yo and 4yo could potentially wear these themselves, reducing the amount of clutter I'm holding.
It's mega-expensive though, especially as I'd need two (and potentially three in the longer term) and I'd like to know if anyone's used it. Is it worthwhile?