There are a variety of board games on the market to cater to every kid's taste, and board games are a great way to bring groups of kids together. Also, if you have a deck of cards, you can keep a group of kids entertained for hours, potentially--especially with games like War, which have a tendency not to end. If you only have one kid, teach him how to lay out a deck of cards to play Solitaire.
Teach your young kids the concept of gratitude and how to express it. This activity, while easy, is exceedingly useful, giving your kids positive things to remember in tough times. Have the kids sit in a circle and pick a kid to lead. The kid should name one thing that he is grateful for, starting with the letter "a." The next kid, to his left, should name another thing for which he is grateful, starting with the letter "b." Continue until you cover the entire alphabet.
Help your kids do dramatic readings of storybooks that you have handy. Assign a character to each kid and, before you start reading, discuss the characters with your kids in terms of their motivations, what their lives are like, what they want, how they feel about things, et cetera. Then, have your kids act out the characters, either by reading the characters' lines with expression or by improvising in character. This can be great fun and very entertaining.
Every kid loves to make things with playdough, but wouldn't it be much cooler to make playdough? Put a smock on your child and help him mix one cup of salt with one cup of flour. Slowly add water and a little bit of food coloring. Have your child mix then knead the dough until it is smooth and elastic but not sticky. Give your child cookie cutters and help him to make shapes and create things. Caution: food coloring will stain surfaces that it touches, so lay out newspapers before allowing your kids to play with the dough.