I found the first 6 months quite straight forward. The next six were a grind and then we came out the other end.
In the beginning it is not too difficult, the y have to get used to holding the violin under their chin and straight across (ie not tilting down). Not a particularly natural position at first. They need to get the bow hold right (check thumb placement and how tightly bow is being held). Intially dd just played the strings with the bow (no fingering) and a mixture of arco (drawing across strings with the bow) and pizzicato (plucking the strings with the fingers). She soon started on fingering on the first two strings, seems to vary from teacher to teacher.
Then you get to fingering and finding the right note by ear. By fingering I mean: first position and second position initially. They involve different placement of 2nd finger. So maybe you are playing first finger, space ,2nd and 3rd close together, space, 4th finger. Or you are placing 1st and 2nd close together. If that makes any sense. If you put your hand flat on the table to try it, you will see what I mean by moving 2nd finger from close to 1st over to lie close to 3rd. That's a bit simplistic but to give you an idea. It is not easy for them to place the fingers close together at first and you need to work on that.
Everything else like dynamics (getting louder, quieter, etc) rhythm, melody is not violin-specific.
The big things is can you hear and find the notes? Either you can do this easily or you can't. I can't. Dd can. I can't tell her if she is wrong but the teacher can. She'll say "I think it's a bit higher dd, no that's now too high, can you find it? Yes, that's it". If you don't hear the notes you play and work on getting them, you won't learn the violin. Then you move further towards the body of the violin to do other notes
I think it's ok if your dc is physically able to cope with the manipulations of the fingers, one hand doing one thing (fingering) the other bowing and if they have a good ear or good instruction to acquire one. Lots of dc learn violin at a very early age, starting around 4 with tiny violins so I think 6 is a good age to start on it.
The violin is very versatile and it a nice emotional instrument too, I think it is a good instrument to learn but not as "easy" say as basic piano where you put your finger on a key and the right note comes out IYSWIM. Not that I'm claiming piano or any instrument is truly easy if you want to master it.