Design a vinyl graphic image for a fundraising poster on behalf of a charity

Design details: We have been asked by a charity based in Surrey who provide enhancements in hospitals for children, to design a poster to put on a wall to promote the charity and announce new projects along with having a call to action to get people to donate, we await a fuller brief but need someone to produce the design for the poster
Target audience: Hospital visitors / parents of patients
Ideas for the visual style: eyecatching and punchy but suited to a childrens' hospital environment
Extra notes: As this is for a charity we would prefer the work to be pro bono but have suggested a £50 fee would be available if required. some of what we do can be seen here http://www.grosvenorinteriors.blogspot.co.uk/