nomerci - you can leave the car seats in your car when you get there as well as one of the prams, then put one child (toddler in the trolley) and carry the baby in a sling or push the pram - slightly awkward but i have done it.

BUT it is 10x worse if you are in a taxi or on the bus- what do you do when you come by bus and taxi and you have to take out the car seats and the pram (for arguments sake, just one pram on this occasion) cart those around as well as push the trolley and then carry the shopping later - not everyone has a maid that follows 10 paces behind them.