Should I Tell a Parent it's Not Working Out?

Hi, I have a daughter who is 16 months and I have two 4 year old boys and a little boy who is 14 months in my care. The 14 month old is the one who is giving me problems. He has separation anxiety, but that settles fairly quickly once mom leaves. The issue is that he cries for EVERYTHING and will not be consoled. Some times his blankie and a 'bubba' work to calm him down but only on occasion. He does not care for me at all and so it's very difficult to bond with him as he is constantly upset whenever anything changes. This could be as simple as the music that's playing or that he is done eating at lunch and snack time. It seems any time he is even remotely uncomfortable with anything he cries and frankly it's driving me nuts. I am as patient as I can possibly be (being 7 months pregnant) and I do not treat him any different than I do my daughter or the other kids - although it is hard sometimes as I do get resentful towards him. He is only here 1-3 times a week and the lack of a steady routine makes it more difficult for him I think. As for me, days when he is not here are like the calm after the storm. I'm nearly at the end of my rope with this child and would appreciate any input you have. I've tried different ways of dealing with him, but i have to pay attention to the other children too. I don't have time to spend all day trying to console this cry baby. He's been in my care now for two months and this has not improved at all. One theory I have is that his parents use the CIO method to get him to sleep - something I do generally not approve of, but have tried unsuccessfully. Something else I should mention is that my daughter was going through a bit of a violent phase for a while there and would pull his hair and stuff. She has since learned that this is not right and they do play together nicely most of the time. Of course there's the occasional toddler quarrel over a toy or something, but nothing out of the ordinary.

Especially considering that in a few months I will have a newborn to take care of as well, I am thinking about telling his parents that it's just not working out and to look for a permanent new space elsewhere after I have the baby, instead of a temporary one for 6 weeks. How would I go about telling them this, especially since I've tried to reassure them that we are working things out with him and that he's been better.

Anyways, I need some help.

Rita