Although infants do not possess the motor skills to create a paper bridge on their own, many infants enjoy watching older children make and test their bridges. Some infants will be able to help 'test' the bridges by placing weights on top.
Infants may also enjoy exploring cause and effect when using a balance scale. Show them what happens when you add weight to each side. Let them practice their motor skills by dropping weights in each side!
If infants will be present while older children are engineering bridges, a grownup should closely monitor the creative process to ensure that infants do not place any small objects in their mouths. Use weights (counters, chips, etc.) that are non-choke-ables, so infants can explore the materials too!