Fritz and Jack sprang boldly on the beam, and danced lightly and rapidly across the new bridge.

Now that the first beam was laid, the difficulties of the work were greatly removed. The second and third and fourth soon followed, and the foundation of our bridge lay ready before our eyes.

We then cut planks of about eight or nine feet long, to place across the breadth of the bridge; but I did not nail them firmly, as I wished to be able to remove them from the bridge quickly in case of danger, to prevent the passages of enemies, whether men or wild beasts.

It now seemed in every point perfect: the supports were firm, and the passage across complete.

The exertion had exhausted our strength; and as evening approached, we were glad to return to the tent, and seek refreshment and repose. Once more we knelt to offer our evening prayer, and to thank God for his merciful care of us during the day. (Chapter VI, "Bridge-Building").

William, Fritz and Jack's father, builds a bridge with his two sons on the island on which they've been shipwrecked.

Wouldn't it be great if we could all just get along like the Swiss family does? This passage shows William and his sons working together; and because they work so well together, they manage to build a magnificent little bridge.

By focusing on the family's collaboration in building the bridge, the passage is showing us all the benefits of working well with others. In other words, there's a lesson that this scene is teaching its readers: knowing how to work as a group is an important skill, and it pays off.

This passage focuses on the action of building the bridge: the laying of the beams, the cutting of the planks, and the nailing.

Children's stories tend to depict people doing things and engaging in physical activity of one sort or another. As readers, children are engaged by action as opposed to thought; by describing the steps that William and his sons take in building the bridge, kids have a task to focus on.