Why the sea is salty?

Since I'm on vacation my kids ask me who put salt in the sea? I did not really know what to reply to them. After having investigated on Google here is the summary that I made them :

There are approximately 4 billion years, on the earth (not yet inhabited), volcanoes were erupting and released into the air a quantity of gas and water vapor.
About hundred million later, the cooling of the earth resulted in the condensation of water vapor. And then it began to rain. Many water was dumped on earth, bringing with them the gases propelled in the air by the volcanoes. This is called acid rain. These acid rain falling on the ground and eroded the rocks.This erosion of the rock created the relief like rivers, seas and oceans. The acidic rain filled in seas and oceans with mineral salts. The main one is sodium chloride, which represents 77% of all the sea salt and is the salt you use at the table.
On average it's considered that the sea contains between 33 and 37g of salt per kilogram of water. The total quantity of salt in the seas and oceans is considered to be about 10 million billion tons!

The asked me too : why the rain is not salty now ?

It's simple, because only water evaporates and not salt. This is how salt can be harvested on rocks or in salt marshes.

Here some pictures taken on the way to the apartment I hope my children will not be sick because they have tasted the salt on the rocks ;-)