I babysit in my home now, so it's a bit different. I have nannyed in the past though.
I think the transisition is a difficult one because it just kind of sneaks up on you. It's not like one day they are a 6mo happy to stare at some toys on the floor, and they wake up a 3yo who needs more structure to the day (or not).
Has the nanny been with you for a while? Maybe just set up a meeting with each one individually to talk about the transision. I would think in your head what would be ideal for you, but not nessasrily schedule out the nanny. You don't want her to feel like she *has* to paint from 9 - 9:30 every Tuesday & Thursday, kwim? Maybe just talk to her about outings (is she driving your baby or walking). If you can find out some schedules (there is story hour at the library 3 blocks away on Wed. from 2 - 2:30). One of hte girls I watch now is 16 months and I don't do outings or anything (since I have more kids and she's only here 2x a week for a few hours). You can also mention stuff you got. Hey X, I just wanted to let you knwo we picked up some crayons for Y she really seems to enjoy them. It's hard to say because 16 months is a vastly different age for different kids. The baby I have is really still a baby. I've seen other 16 month olds who are definatly toddler in their interests and abilities. A lot depends on the kid.
When I have younger toddlers my basic schedule is something like this (just for an idea).
7:30 - 9:00 - arrive, play with toys
9:00 - snack
9:20 - book / color / some type of activity
10 - 11 park
11 - nap
1 - lunch
1:30 - activities in the house.
3:00 - park again (sub backyard but we are in an apartment. snack in park).