I conditionally baptized my infant grandson in the hopes that my daughter would convert and have him baptized. Did I baptize him validly?
Provided you used water and the valid sacramental form the Church prescribes, namely, baptizing your grandson “in the name of the Father, and of the Son, and of the Holy Spirit,” you validly baptized him. There is also the issue of intending what the Church intends, which is also needed for a valid baptism. Some might argue you didn’t have this intent because you only intended to conditionally baptize him as a protective measure, not actually baptize him.
I don’t think such an argument has merit, because conditional baptism takes place only when there is doubt about whether a person was actually baptized, and so the intention of one who conditionally baptizes is to make sure a person is actually baptized.
The question becomes whether you should have acted unilaterally in baptizing your grandson. In case of danger of death, such a baptism would be morally permissible. In the absence of such a condition, which seems to hold true in your grandson’s case, since you mentioned no serious illness, you should have deferred to the rights of the parents—in this case, your daughter and her husband if she’s married—and then trust in God (see the Catechism 1257-61).
At this point, I would tell your daughter what you did and have a fellow faithful Catholic whom she also greatly respects with you when you do, in case your daughter becomes angry with you. In any event, ask her forgiveness for violating her parental rights but convey you were genuinely looking out for your grandson’s temporal and eternal well-being. Then make it a habit to pray for your grandson and your daughter daily and seek to be a regular part of their lives. Your daughter may want some distance for a while and only want you to interact with her son provided you don’t do anything religious. In that case, quietly pray while you are with him and his mother and trust in God for the long term.