As others have said, immersion is definitely NOT illicit. I don’t know how the Ritual is written in other countries but when you read the Canadian
Rite of Baptism for Children you realize that immersion is presumed. I was quite surprised when I read it the first time.
We offer parents the choice of immersion or pouring. I’d say about 25% opt for immersion but our Pastor wishes it was 100%.
Why did immersion disappear from western churches? Off the top of my head I can think of two reasons: lack of running water in churches, freezing temperatures. Unless you have a
flowing font you have to improvise. We have a plastic bin inside a large wicker basket. It sits on a low table beside the traditional font to make the point that both methods are normal. It takes a lot of footwork to fill that bin on Sunday morning before Mass, going back and forth from the kitchen to the Sanctuary with pitchers of water.