When you read Acts 16:33... is there something in your version of the Bible that specifically omits children below a specific age?
your own question gives the answer:
Acts 16:29 Then he called for a light, and sprang in, and came trembling, and fell down before Paul and Silas,
Acts 16:30 And brought them out, and said, Sirs, what must I do to be saved?
Acts 16:31 And they said, Believe on the Lord Jesus Christ, and thou shalt be saved, and thy house.
Acts 16:32 And they spake unto him the word of the Lord, and to all that were in his house.
Acts 16:33 And he took them the same hour of the night, and washed [their] stripes; and was baptized, he and all his, straightway.
it isn’t age, it is BELIEF
Can a month old infant believe anything?
Should you trust a 4 year old when they say they believe something that they have no idea happened?
If a small child can express a belief and back it up with what they were taught...then they believe
but a baby...that is clearly not Biblical, nor is some sort of grace applied to anyone who is baptised, nor is salvation through baptism in any manner