thanks for the tips! We ended up using a handlebar basket, which turned out to be very handy. Yes, I know that feeling - I'm also usually getting to play the role of the mule :)
Btw we upgraded to 20" proper last week, this time we opted for an Islabike Beinn 20 Large. Also very lightweight, also very British...and one of the few producers offering a 1:1 gearing ratio in the first gear (32x32). That was actually the tipping point for me. Isn't it crazy that the bikes for adults get OEM'd with something like 32 F 50 R, while the groms have to deal with 36 F 28R ?