I had the same problem with my son except is was kinder.  He used to get hysterical.  I went and let him pickout a small keyring, and I sewed it inside one of his pockets, and told him that when ever he felt sad or missed mummy he just had to feel it, and it was like a big hug from mummy.

Hope it helps.

My friend's son took a photo of his family to dacare and anytime he got upset he could go and get the photo. It might elp your son, it's worth a try anyway.

I had the same problem with my kids when they first started daycare. Is this the first time your son is going to daycare and leaving your side? How often is he going? My daughter who started at 2 1/2 years was the hardest to settle even though it was only 1 day a week. The moment she knew it was a school day, she would be so clingy and hold a tantrum all the way to the school, i basically had to carry her from the car to her class kicking and screaming... lol.... All i can suggest is to just keep up with the routine you have to take your son there, stay with him for a little bit and then explain that you have to go but will be back to pick him up, i know its hard and you feel upset leaving him because he is crying but just stay calm and dont show any emotions that your sad to leave him. It took my daughter a year.... yes a year to finally be happy to attend with me dropping her off without crying at all. The teachers tell me, once i leave she would immediately settle and stop crying and be happy to play with the toys or whatever activity they have planned for the day. If you son is not having any problems after you leave and is happy during the day, then you shouldnt have to worry.