There are many churches that offer full immersion baptism....a few that come to my mind are:
Born Again Christians
I am a member of the Christadelphians. We practice full immersion baptism, but we just don't let anyone get baptised.
Baptism was preached by Jesus for us to repent of our sins, understand God's word and commit to following Him.
For these reasons, babies cannot be baptised - they don't sin so cannot repent, they don't know God's word or understand it and cannot commit to following him. You have to be old enough to understand the meaning of baptism.
Baptism is symbolic of death. When we are immersed in the water, our old sinful self "dies", our sins are washed away, when we are brought up out of the water, we are a new sinless person. God forgives our sins during baptism.
This doesn't mean that now we are without sin and absolutely saved - we can and still do sin after baptism, but now we have a covenant with God that we have a chance at salvation, whereas those not baptised do not have that covenant.
If you get baptised without understanding the commitment you are making or understand God's words, then you are blaspheming and are committing a worse sin than if you never got baptised. It is not something to just do, you have to understand what you are doing and to commit to God sincerely.
Usually when a person in my church wants to get baptised, they are interviewed by the elders of the church, to ensure they have the proper understanding of scriptures, and know what baptism means, how it will affect them, the commitments they have to make to God, etc. That way we are ensured that they are prepared and understand what they are doing.....that is why we recommend that it only be for adults or older teens.