How can the sentences best be combined to logically show that the two events are happening at the same time? The children swim in the pool. Their parents watch them from the deck.

The children swim in the pool after their parents watch them from the deck.
The children swim in the pool although their parents watch them from the deck.
The children swim in the pool, but their parents watch them from the deck.
The children swim in the pool as their parents watch them from the deck.