To answer a few questions:
Toddler skills using books are color coded, writing, logic, and painting. If left lying around, toddlers can read them on their own.Children Teens and Parents can read to Toddlers and reading to them in the library gives an added relationship/environment boost. The Jimmy Sprocket series is not part of the skill sets.
As for keeping track of skill levels, especially for adults, most of the hidden skills get those yellow announcements every 3 levels or so. That said, you'll see at least 2 announcements on hidden skill progress. I've seen it for diving, haven't seen it yet for dancing.
The blocks set for toddlers boosts logic. The child's block TABLE boosts handiness for children, not toddlers, but the table does provide social interaction between toddlers who have learned how to talk. The xylophone boosts music, the stuffed animals once boosted charisma in sims 2, but as far as sims 3, I'm not sure.
