Our DGD has been going to nursery 3 days a week (one half day, two whole) since age 12 months. She's now just coming up to 18 months and loves it.
She was very clingy until mum went back to work, and there were tears at nursery when she'd drop her off. But so were half the others being left by mums!
She settled withing two weeks and stopped crying when dropped off. Whilst at nursery, she got used to be carried about by lots of different teachers before walking. So much so to the point when we picked her up, her arms were reaching out to me before I got to her room's doorway!
She is walking now. We bring her here on the half-day and have a great time. BUT as soon as mum or dad shows up to fetch her from ours... she only wants them to pick her up, but does not cry, just reaches and reaches until they take her and cuddle.
Sorry for the epistle, but I think it's normal to be clingy and fuss. If loud and long, maybe the routine isn't fixed in their head yet. And, some children I think are just very sensitive. 