Many years ago, I believe it was the NSPCC that refused a donation from an event to raise money where women dressed as "sexy school girls" or similar. Obviously, a charity concerned with the safety and welfare of children, many of whom have been sexually abused, would not be pleased to be associated with an activity that involved stylising women as sexualised children.
I think there is a difference between the fundraiser mentioned in the OP and the Calender Girls/original WI campaign. Images of the WI women were of them doing ordinary things like cooking and gardening. Most weren't looking into the camera. They were nude, but not styled or posed in a sexualised manner. They weren't intended to be objectified and the models did not fit the "type" used for traditional "pin up" style calendars of sexualised, naked women.
I can't imagine the plan is for the women of Sugar Lounge to be photographed with discreetly placed crockery as they make jam, scrappbooking or other "ordinary" activities. The images will be overtly sexualised and objectifying. The company profits from the sale of women's sexual services and probably see this as an opportunity to enhance their "social responsibility" credentials. Even if "every penny" of proceeds (as they suggest) goes to the charity, they are certainly hoping the tie in will be good for business.
It's quite likely that some of the patients on the children's ward will have suffered sexual abuse. There is evidence of increased levels of sexual assaults in the vicinity of "gentlemen's clubs." The two don't sit very neatly together.
I agree - set up an alternative, and perhaps those locally could register their concern with the hospital about the message they are sending out in accepting proceeds from this calendar and this company.