Visit a public school and a private bilingual school. The smiley stickers for doing a good job are also useful. My personal experience has been that school supplies are in short supply all over Mexico. English readers are fine, but they will, in all likelihood, not be in sync with the books in use. These items can be purchased locally and given as gifts.
Money is always the appropriate fit.
Don't waste your time picking out gifts for hotel staff, who would appreciate more an adequate tip as a show of your largesse. Tips can be more easily apportioned among hotel staff than a pair of shoes. Think real hard before doing this, and consider how you'd feel if some rich Arab bestowed solar calculators, writing instruments, and Arabic readers upon a poor school in West Virginia. I'm sure your intentions are very good, but think about the impact first. Please remember when you come to Mexico, although there are certainly needy people here, poor folks aren't contestants on the Queen for a Day show.