Horrified children look on as lollipop man in his 70s struck by car on school crossing
(www.manchestereveningnews.co.uk)
Lollipop man or lady is what's its always be known as. It is dignified as people are very grateful to the people who do these jobs and its an affectionate name.
Crossing Guard sounds american, and a bit hostile to be honest. Lollipop man sounds warm and kind, which is also nice for children. The official UK government name is "School Crossing Patrol Officer" - no thanks.
Edit: also Lollipop lady/man is also used in Ireland, Australia and New Zealand apparently.