My four year old son is all into Star Wars (Clone Wars especially) and superheros, plus sports and remote controlled cars (the simple ones, of course). He enjoys his legos, but we don't buy him the Duplo legos, because he prefers to make space craft out of the star wars sets (the smaller ones he is able to build himself following the picture directions, and then tears them apart and builds whatever he wants). Choking hazards should be taken into consideration, depending on your child. For the one year old, I'd say anything with bright and colorful buttons!
When my son was in that age range, I used to take him on a trip to the toy store, and see what he gravitated towards. I would tell him ahead of time that we had to figure out what to buy for another child relative (or buy him something small), and we would quickly go through the aisles. Alternatively, I would recommend Duplo for the 4 year old, a marble track toy, where you build with chutes and tunnels for the marbles for the 7 year old, and for the one year old, push toys and a box with little doors on it with lots of different fasteners.
I have a 3 1/2 and 7 1/2 year old boys and they both play with the Fisher Price Imaginext sets and love them as well as the Fisher Price Train Geo Trax sets. Also anything where they can build, Duplos, Trio block sets, lincoln logs, knex keeps them busy for ever. For the one year old girl Fisher Price Little People sets are great something she can grow with and something that the boys can play with her and books babies love board books and they can enjoy those for years as well.