property rights of my 1st wife children towards my mother's property?

If the property was self acquired by your mother, in such case your children during your life time will have no right on the said acquired property.

However if the property is ancesteral property, the your children will automatically have right on the property on their birth and now can file suit for partition. The  pre-requisite condition required for a property to be Ancestral property is that it should be owned by the great grand father followed by the grand father, father & present generation all in this linear arrangement, living & enjoying the property. The property should not have ever partitioned & share in it distributed to any of the Hindu Coparceners as in any linear generation as mentioned above, in other words, it should be intact single property which is being used jointly by all members of the Hindu Joint family.

Therefore, all property inherited by a male Hindu from his father, father's father, or father's father's father, is an ancestral property. The feature of inheritance of ancestral property according to the Mitakshara law under Hindu Succession Act is that man inherits from any of his three immediate paternal ancestors, namely, his father, father's father and father's father's father is ancestral property as regards his male issue, and his son acquires jointly with him an interest in it by birth. Their rights attach to it at the moment of their birth