The user does not have to fill in the date/adults/childs/rooms, they are optional. The user can also search with only filling in the destination (left box).
How would you visualize that?
I would suggest the dates and rooms fields are defaulted to say "No Specific Dates" and "No Specific Room Size" (or something along those lines).
That makes it clear that they are optional and the user can precede without selected them.
When the user clicks either of them, you can then allow them to specify the values as you currently do and they will show relevant text to reflect the selected values.
Don't forget to include a way to reset them back to "No Specific..." values too.
I think there's not only just a single issue or solution to consider here.
the importance of the Search field should be given to the user via
Search button and the rest of the secondary important information can be chosen same to give the user the ability and feeling of selecting defaults,
Besides having the aspects mentioned above, users would intuitively see defaultly selected values and may apply change if they want.