My sons are 21 months and 5 months. They've both been going to creche since they were 3 months old, for 2 days a week. While it's still hard to leave the yougest one, he smiles as soon as he sees his carers so i have no problems leaving him.
His big brother has never had a problem going, in fact we walk in the door and he's off to the toys straight away! I kiss him bye as he plays, and as i reach the door i say goodbye again. He turns, yells 'bye-bye Mummy', blows a kiss and it's straight back to whatever he was doing!!
Take heart, it will get easier! I bet if you hidaround a corner, or snuck back in to have a peek 10 minutes later, they wouldn't be crying anymore. The carers are usually excellent at distracting the children and involving them in activities until they are happy to be there.
Dette, DS 06.03, DS 10.04, DD 03.06 & Due Sept 07!