The time has come. The time is now.
For ages, Adam and I have been planning a kid swap once they were old enough: one free morning for me and one free morning for him while the other watches both toddlers and the rest of the kids are at school. This is week two, and so far, so good. The swapped baby gets a little upset when they separate from their mom/dad and when they rejoin them, and there's an occasional moment of where's-my-mama despondency, and the occasional sippy cup squabble, but really, the boys are both doing pretty well.
Today, Xander, Luke and I went for a walk all the way around our block (amusing with two 17-month-olds on foot) which featured many sticks and puddles, and later Luke taught Xander a new word: MINE. Most excellent.