K.J.
I had my son last March and as soon as it was warm enough to get him out in the stroller, I did. I thought fresh air would be good for him at any age as long as he was dressed appropriately. I'm not sure there's a "waiting period" or anything for taking them out as long as they are healthy. He's almost a year now and I've never left him with a sitter except for Grandma and Grandpa, and only 3x with them...but I have friends who've had sitters after only a month or two. I think it depends on the parents, but I think either way is okay.