my son had this problem, it use to break my heart everyday to take him to school and leave him there, from the moment he opened he's eyes in the morning he started crying and working himself up not wanting to go to school, he'd follow me round the house while i was getting ready, he'd be sick aswell, somedays it drove me nuts it was so frustrating, but all i could do was keep re-assuring him that i would be there to pick him up at the end of the day, i also told him if he needed me while he was at school i would drop everything and be there in a flash, the teacher even let him pin my mob no: to the notice board so that he could see it, this was re-assurance enough,i was never once called to come & get him, i still had the bit in the morning, it was the actual seperating that he hated, sometimes the teachers use to have to force him in school, all i could do was smile at him and let him see that everything was ok(inside it was so upsetting to see him like this) but i knew if i took him home once that would be it,it took a while for him to get over this but we got there in the end with a lot of re-assurance and patience, every now & again he still has a moment of panic, but i just let him know where i'm gonna be during the day give him lots of hugs and he goes off quite happy,he even goes to parties now which at one time he wouldn't do that unless i was there to, now i'm glad to say i cramp his style.
I have worked in day care centers and have run a home day care, the best thing you can do to help your son is to keep on telling him you will be picked up at this time. Tell him about a half an hour later than you plan on getting him. Always better early than late. Tell him you alternative pick up. " if I can't get you I will have Grandma come for you". If you know in advanced tell him so and so will get you today. Also talk to the providers about your sons feelings. Most children are a little sad after they are dropped off but then get in the swing of things and forget they are sad. Because of this a lot of providers are unaware of how upset somme children are. I have also found a small photo book of their family helps. Take pictures of you and your family with your son, especially the things you do right after day care. Let him bring it to school, show his friends and teachers. This way he can feel close to his family and be reminded of things you'll be doing after school. You shouldn't have to do any of these thigs for very long ( a couple of weeks). I hope he starts to feel better about school soon.
I work in a preschool and it is difficult for the children to separate from their parents. It is upto the parent to make it a positive experience the 'good byes'. Sing some of the songs they sing in the car on the way when you get there give your child a kiss and hug and ask them to wave to you in the window. Ask them to paint a picture for you. Tell them what time you will pick them up and be there at that time. Also smile a lot and don't show your concern. It is mostly about routine and you will find once your child knows the routine they are really comfortable. Usually if a child cries for more than 20minutes at one time we call the parent if they are 3 but it does depend on whether it seems to be a real sadness or a tantrum. Sometimes we find that the parent needs more reassuring than the child. I have one child who cries and as soon as his mother leaves is laughing and playing within a minute. For us the performance is amusing and yet frigtening jekyl and hyde. Be patient, we know you miss your child but it is what you have chosen to do and if you trust the teachers feel comfortable in their care.
Try to respond to this with equanimity; your emotional response is the most important thing for you to address. It sounds like the teachers are fine; they have seen this a million times. Your idea of three days each week is a good one. Ironically, some children who display this sort of anxiety actually require more, not less, time in the setting so that it can take hold as a routine component of their weekly structure. Try to think of your son's response as a version of normal and it will likely trouble you less.