1. Fun. My husband and I both get into building. Duplos belong to toddlers, and toddlers are into parallel play. That means Mommy and Daddy have some time to try our hand at being creative in form or making interesting patterns. The kids have some fun too.
2. Social Interaction. Sometimes we did build houses together, or we tried to build the tallest possible tower. For a while, my one-year-old would knock over her brother's towers. As long as he was in on the game, it was fun for all.
3. Fine motor skills. The effort of pushing the blocks together builds strength into the pincer grasp of little hands.
4. Colors. "What color is this?" "Would you hand me a blue block?" I would choose two colors to introduce and ask about two or three times on a particular day. In the context of parallel play, we found an effortless learning opportunity.
5. Sorting. As we built towers, my kids soon followed my lead in building towers that were all one size of block. Later on, they began to try to build edifices that were all one color.
6. Counting. "Look, your tower is five blocks tall, one, two, three, four, five." Either the conversation ended there, or we counted, and counted, and counted. The mystery of developmental cycles!
7. Basic physics. Yes, it is significant that they know that a tower with a wide base and narrow top is more stable than one with a narrow base and wide top.
8. Safety. Duplos can be pretty thoroughly disinfected, and they're tough to swallow. These are wonderful traits if there's a little one crawling and mouthing.
Fair well, excellent toys!
Update: That same boy just passed his eighth birthday, and while the LEGO's are in heavy use, the DUPLOS have only multiplied, much to this mama's delight.