I went to a bonfire when DS was 7 months old. It was only a km down the road and my sister sat with him.
I had about 4 beers but I made sure I had 2 large glasses if water in between each beer. I didn't even feel tipsy! Lucky, as DS wouldn't drink anything from the bottles that my sister offered so I had to feed him when I got home anyway. I felt a bit guilty but figured as I had so much water to drink that I wouldn't have had much alcohol in my system anyway.