desde niño

man and boy

fue

1. third-person singular preterite indicative of ir
2. third-person singular preterite indicative of ser

creyente

1. believing
2. religious, pious, devout

en

1. in, at, on
2. in (a time)
3. in (a language)
4. used after some verbs and translated by various prepositions in English
5. in (in various expressions)

el

masculine singular definite article; the

cristianismo

1. Christianity
2. baptism

desde

1. since
2. from (a location)
3. starting at (a quantity, such as a price)

niño

child, boy