We had a thread on this a while back and someone actually checked with the police who said it is not considered abandonment or being left unsupervised in this situation. Probably because it's only a couple of minutes and bub is within sight - otherwise we'd all be getting fined for carrying one sleeping child into the house and leaving the other one in the car for a minute till we came back for them ay. Unless you're incredibly fortunate and always have someone else with you.