Why do Catholics & some other sects believe in child baptism when no one in the Bible was baptized as a child?

You're supposed 2 get baptized when u accept Jesus as ur Saviour, n realize he died on the cross 4 u, n rose. u gotta realize the importance of it cuz ur proclaiming to the world, u r followin God n symbolizing when he goes in the grave (u go in the water) n when he rises (comin out of the water) ur old self dies, ur new body rises. how can an infant understand all this. if he/she can, then they ofcourse can get baptized, but if they dont...? n nowhere in the Bible does anyone just get sprinled w/ water, they r fully submerged into it. so where did the sprinkling come from?