Take a big vessel put into it water and sugar. Mix well and boil it at slow flame till it dissolves. Keep stirring intermittently. Let it be on flame till you get, a one string consistency of sugar syrup. Switch the flame off. Keep it warm.

Next take mangoes. Wash them well. Take out the pulp from the mangoes and blend it smooth. Put this mango extract and lemon juice into the warm sugar syrup. Mix well.
Let it cool. Our mango squash is ready...

Shelf life of this mango squash would for about 2 weeks. Keep it in a clean airtight sterilized container and refrigerate.
Do not use watered hands/ unclean spoon while using it. If you do so, your squash will spoil.

If you want to store it for longer time you can use sodium benzoate. This is a preservative. But I prefer not to add any preservative as it's homemade and made for my toddlers.

So take bit care, while using it and you can get a preservative free mango squash.