We went to a 21st party when he was 6 weeks old which was held in someones back yard, just made sure he was rugged up and he was either nursed by someone or sleeping in his stroller and he was fine and happy.
Zander was at a BBQ at 1 week old, although it was March so not too cold. He was also at my sister's 21st party, on the harbour (it was a cruise) when he was around 10 weeks old as well. I was starting to think I was the only one!