When you pictured your children interacting, you imagined they'd laugh and giggle and be each other's playmates while you happily congratulated yourself for not raising children like the neighbor's, who constantly threatened each other with physical violence. Fast forward a few years and your own sweet angels are constantly trying to exclude each other or squabbling over an empty tube of toilet paper while slinging touching phrases like, "You ruin everything!" and "I hate you!" Bonding and sibling friendships often require some parental facilitation, but the payoff will be worth it.
A constructive activity that lets each child complete her own task while working alongside the other is a good way to begin a bond between siblings that get along like oil and water. For example, let the kids use the furniture cushions to make their own forts in the same room so they're forced into reasonable proximity. Encourage them to "host" each other and show the other sibling the different areas of the fort. Or, have them each build a castle out of blocks or plastic interlocking blocks. Tell each child to think of something nice to say about the other's construction. If your tykes are generally cooperative, they can build something together. Note that building a single construction will only work if your kids can reliably play together for more than few minutes without screaming, crying or wrecking the other's creation.
Helping Each Other
Encouraging your children to help each other is one of the most effective ways to help them bond. Even if it means you still have to supervise, ask the preschooler to help the toddler put on her pajamas for bed or put on her shoes in the morning before school. Also, ask the younger one to help the older child set the table or feed the dog. Make sure the younger ones help out the senior kids as much as the older children help the younger siblings. Otherwise, the older child may begin resenting her role of built-in babysitter and further dislike her siblings.
Baking is a great activity for siblings who get along, or at least are civil, but who aren't bonded. Under close supervision, let the children take turns stirring, pouring and shaking. Let the older one help the younger child by holding the bowl steady while he stirs the mixture. With your guidance, older toddlers and preschoolers can knead dough or help decorate cookies. When the time comes, the siblings can enjoy eating the creation together.
Surprising Each Other
Let an older sibling choose a new T-shirt for a younger child. While grocery shopping, ask a younger one to pick out some fruit she thinks her sister would like. It's okay if they hear the other's suggestion; they might be pleasantly surprised how much their siblings know about their preferences. Encouraging them to pick surprises for their siblings gets them thinking about each other in a thoughtful and caring way. Remind the recipient to thank the sibling who chose the surprise, even if it wasn't her favorite or first choice.