I'm a doctor and I've worked in a children's burns unit and... well, that's all I want to say about that: it was many years ago and I'm still haunted by some of the things I saw.
Those of you who think this is a big joke and the OP is being precious need a BIG wake-up call. If you think it's silly and OTT to worry about scalds from hot drinks then, frankly, I wouldn't want you anywhere near my children.
People are very attached to their hot drinks at toddler groups so I think it's unrealistic to try and get them to stop, but balloonslayer has mentioned some very good, sensible precautions to take.
In the same way, most of us would be reluctant to give up driving but will use seat belts, defensive driving techniques and other safety measures to reduce risk - the point being that you acknowledge the risk and take it seriously.
By god I need my coffee some days but I'd give it up in a heartbeat if other parents in our group were keen. As it is, I just go without if the room is too crowded to handle a cup safely.
My inalienable right to a cup of coffee vs a permanently scarred child - it's a no brainer as far as I'm concerned.