is it ok to ban liquid items in planes even the milk for children

It is for safety of public only and for the safety reason we have to co-operate.

If it is for the safety of everyone flying, then yes it is okay to ban liquids being brought on to a plane. For children, you can always bring powdered formula and ask them for a bottle of water to mix it with. I believe the ban is just for brining liquids on to a plane, but they are still serving liquids so you can still get juice, milk, water and sodas from the flight crew.

There are security reasons behind the ban of liquids on hand baggage only. You can always carry them in your suitcases. And for your info baby products including milk is allowed on hand carriage. you may have to taste before you can carry tbem