Sharing is a word that is a double-edged sword. It can bring tears of happiness to a parent's eyes or tears of anguish to the eyes of children.
With such a small age difference between my two littlest children (my son turned 3 in June, my daughter was 1 in April), most of the toys are interesting to both of them. For example, both children love playing with stacking rings. My daughter first starting using them when she was crawling. She would put one in each hand as she would slide across the floor. My son uses them to enact the television show "Color Crew" (Baby First's Color Crew). Both enjoy stacking them but sometimes sharing doesn't work out so well. Sometimes they both want them and other times my son wants my daughter to play with them with her but she is too busy on her own.
Another toy of contention in our house are Lego bricks. They have a total of three sets of the Duplo. My daughter is fascinated with pulling them apart - working on those fine motor skills. My son likes to build laser guns and light swords based upon a popular sci-fi video game as well as build cakes. He first built a cake for me and said "Happy Mother's Day." A little late, but very meaningful to this emotional mommy. Of course, when his sister wants to take apart his creations, he has shed a lot of tears himself.
As they learn to play with each other, I see them wanting to play more and more together. For example, my son has been building tracks for his Go Go Smart cars and my daughter has been using the cars on those tracks. And when he colors, she has to have paper and crayons, too. I think I am in for a lifetime of them sharing with each other and their older brother.