To be honest with you, I had never heard of any priest or deacon baptizing children with “we baptize” instead of “I baptize”. But of course, I don’t go to any baptisms done by another deacon or priest, so why would I hear it?
But I have never heard of anyone saying that so and so priest or deacon baptized by saying “we baptize...”.
So how common is it? And why use “we” instead of “I”? Who is the “we” anyway?
I have heard of “I baptize you in the Name of the Creator and of the Redeemer and of the Sanctifier.” That was roundly condemned about 20 years ago by Cardinal Law of Boston who told the improvising priest to go and rebaptize every one he baptized using that formula.
But I have said it before and I will say it again, if priests and deacons are using invalid formulas to baptize, how much more Protestant ministers? Thus I recommend and I will begin to baptize conditionally Protestants received into the full communion of the Church. Protestants are more freewheeling than most Catholic priests are when it comes to improvising. Congregationalism runs deep in Protestantism and doing your own thing does too.