It is very hard to translate. Like told before, there are some oldish words that you can't find from a dictionary. I'll give a try to translate it, but I'll do it pretty straightly for that you could get an idea about the song.
First I explain those words you couldn't get a translation for. For those oldish words I also give the correct (new) word.
kulkevi
kulkee, to go
hänt
häntä, him / her
vie
takes (to somewhere)
näy
can't be seen
vierellä(because of?)
by (one's) side
käy
goes, walks
liukaskin
(also) slippery
lie
may be
oi
oh
pianhan(piano?)
soon
vois
could (be)
ois
would be
siltikin(bridge?)
although, still
Then the whole song. But remember, this translation is not musically good, because you just can't translate a song directly to another language. It is straigthly translated for the meaning of it. I translate it like the child was a girl, but "she" could also be "he".
Maan korvessa kulkevi lapsosen tie
In the wilderness of land goes a child's way
hänt ihana enkeli kotiihin vie
A lovely angel takes her home
niin pitkä on matka ei kotia näy
The journey is so long, she can't see home
vaan ihana enkeli vierellä käy
But the lovely angel walks by her side
vaan ihana enkeli vierellä käy
But the lovely angel walks by her side
On pimeä korpi ja kivinen tie
It is dark wilderness and the way is rocky
ja usein se käytävä liukaskin lie
And often this corridor may be also slippery
oi pianhan se lapsonen langeta vois
Oh, soon could this child fall
jos ei käsi enkelin kädessä ois
If she was not hand in hand with the angel
jos ei käsi enkelin kädessä ois
If she was not hand in hand with the angel
Ja siltikin mustia verkkoja vaan
And still only black nets
on laajalle laskenut korpehen maan
Has widely fallen into the wilderness (of the land)
niin pianhan niinkin tarttua vois
And soon could she stick to them
jos ei käsi enkelin kädessä ois
If she was not hand in hand with the angel
jos ei käsi enkelin kädessä ois
If she was not hand in hand with the angel
That's it. Beautiful song.
Edit: Just noticed that there's one more verse:
maan korvessa kulkevi lapsosen tie
In the wilderness of land goes a child's way
hänt' ihana enkeli kotihin vie
A lovely angel takes her home
oi laps' ethän koskaan ottaakaan vois'
Oh child, you could not ever take
sä kättäsi enkelin kädestä pois
Your hand away from the angel's hand
sä kättäsi enkelin kädestä pois
Your hand away from the angel's hand