i work in child care and i advise that you DO say good bye, and that you will be coming back. (for the reasons mentioned above already). at first they wil cry but it is better that way, cause if they have an explanation and over time it is carried through they will put two and two together and understand. better than being distracted then 5 -10 mins later look up to show mummy something and they are gone. try and make a fun ritual at drop off time, like waving through a special window, or something like that. ask you day care teacher if they have a special place to do that sort of thing, often there is. i know it is really hard, my DD still cries at times when i have to go.