I always buy my DDs a pair of Birkenstock Roma sandals for the summer - nice and supportive, can walk for ages in them, and pretty colours.
Have bought the younger DD a pair of Rios instead this year (a little bit daintier than Roma) but the older one wants Gizeh (www.amazon.co.uk/Birkenstock-Birko-Flor-Style-No-Sandals-Regular/dp/B000KBZSPG/ref=sr_1_fkmr0_2?ie=UTF8&qid=1303895524&sr=1-2-fkmr0) instead - I'm reluctant as I'm not convinced toe-post sandals are supportive enough for a 6yr old (but our very good local independent shoe shop do sell and recommend them) - what do you think?
Have also bought a couple of pairs of frippery sandals (Next, H&M et al) for parties/meals out etc. - but the Birkies are their walking/day out sandals if that makes sense...