Formal:
* Sanggol na lalaki (literally "infant male")
* Sanggol na bata (literally "infant child", can be used for both boys and girls)
Informal:
* Bata (simply "child", can be used for both boys and girls)
* Sanggol (simply "infant", can be used for both boys and girls)
* Baby boy (the English phrase is often used)
You can also use endearments like:
* Bunso (youngest child)
* Anak (child)
* Baby
Ultimately, the best way to say "baby boy" in Tagalog depends on the specific situation.