C.C.
Hello! I can not speak from a mothers oint of view, but I will share something with you...When my father was 47 he had a son, which was a half brother to me. When my half brother was 2 to almost 4, he did almost the same thing. Even though I visited almost every day from the time he was born, he was so upset if they left him with me, and even if I stayed there! He is now 5 and does a little better. I know it's common, and the advice is probably the same as you've heard before...have the sitter distract him from crying. Start a routine when you leave (maybe a book that you all three read together, a kiss, a high five, then out the door), be strong.
I am a SAHM to a 14 month old, who is VERY attached to me, so I'll be interested in reading the responses to this questions for later advice. Good Luck!