Just to back up what everyone else has said:
Code Of Canon Law Ref:
And more germane to the question:
Can. 861 §1 The ordinary minister of baptism is a Bishop, a priest or a deacon, without prejudice to the provision of can. 530, n. 1.
§2 If the ordinary minister is absent or impeded, a catechist or some other person deputed to this office by the local Ordinary, may lawfully confer baptism; indeed, in a case of necessity, any person who has the requisite intention may do so. Pastors of souls, especially parish priests, are to be diligent in ensuring that Christ’s faithful are taught the correct way to baptise.
Can. 862 Except in a case of necessity, it is unlawful for anyone without due permission to confer baptism outside his own territory, not even upon his own subjects.
If, as has been surmised, it is merely the case that the parents of your grandchildren do not seek baptism for them, that *per se *does
not constitute
necessity.
If a case of necessity should arise, and were your to baptize your grandchild(ren) (or anyone else), this should happen:
Can. 877 §1 The parish priest of the place in which the baptism was conferred must carefully and without delay record in the register of baptism the names of the baptised, the minister, the parents, the sponsors and, if there were such, the witnesses, and the place and date of baptism. He must also enter the date and place of birth.
Can. 878 If baptism was administered neither by the parish priest nor in his presence, the minister of baptism, whoever that was, must notify the parish priest of the parish in which the baptism was administered, so that he may register the baptism in accordance with can. 877 §1.
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