Many organizations are ready and willing to receive such direct "in kind" donations. How to find them? One easy way is to visit Family Travel Network, which has done a huge research job, identifying schools, orphanages, charities, and other organizations that welcome donations and have set up easy ways to drop for travelers to drop off their gifts-- in Mexico, Jamaica, and a bunch of other countries.
Read, for example, how you can easily help others in the Dominican Republic, which is home to so many popular all-inclusive resorts: bring notebooks, children's scissors, molding clay, lego bricks, backpacks, calculators -- you name it, and the DREAM Project will be happy to have it, and -- if you're near Cabarete on the north coast -- may even come to your resort to pick up the items.
Or if you're visiting Caso de Campo in the DR, that giant resort works with community programs and several charities. It even has a program to help guests do some volunteering during their stay; teens can even earn a certificate for service hours.
- "We simply ask that anyone who is coming to vacation in the Cancun area bring with them, some toys, school supplies, or other appropriate gifts for these children."
Many More Countries
Family Travel Network has many more suggestions for direct donations in the DR and Mexico, and also has similar information about schools, orphanages, and other charities ready to receive in-kind gifts in Aruba, Jamaica, Mexico, St. Lucia, and other countries - see all these resources for Bringing Donations on Your Trips.
See also some thoughtful tips about direct giving (--scroll down): random gift-giving, and unannounced school visits, can have effects we would not intend.