The welfare staff are the people who patrol the form rooms during lunchtime. There are some quite awesome welfare staff, such as the one who consented to marry at least two students, the one who refuses to high-five people on fear of getting reported for some reason, and the one who will let you into the canteen with your shirt out and top button undone whilst you are blatantly eating hot food.
The welfare staff are lovely and are often up for a chat, and will happily partake in whatever nonsense you are doing - including: throwing Christmas baubles onto the balcony, playing table tennis, and kicking around a traffic cone (much to Mr Reeves' dismay).