I had my mom, aged 69, babysit my infant son, and also had three grandma-aged nannies in the first year and a half. The con is that it's hard to tell older people what to do. The pro is everything else, I'd say.
When you want MIL to do something, couch it in deference to the pediatrician. If necessary, betray your astonishment that such findings have materialized. So like, you kind of side with MIL against the pediatrician, but take his/her advice OF COURSE, and so here you all are, wiping front to back. That's my take on grandma-aged infant care: what they lack in trainability they are up for in knee-jerk deference to physicians. Of course if that's not your MIL, then it's not, so not helpful.
But in general, grandma-aged women are a really solid infant care choice. I know what you mean about the slip-and-fall. I actually had to let one caregiver go because she'd had fainting problems, and I just thought if it would happen with the stroller at a crosswalk, I'd regret it. So you have to look seriously at any health challenges grandma has. But it'll probably be great. The dedication shown by a grandmother is absolutely heartwarming. Very reassuring to a mom too, to have your own mom take care of your kid. That extreme level of investment they have, vs. a daycare worker off the street is really palpable.
