I have taken seriously the idea of having a recital in December. I took the chance of accompanying the kids for my son's group in kindergarten. But I didn't think it through so I'm facing some problems, of course

I know... a beginner has crazy ideas

Please bare with me.
They are singing three songs I've been practicing:
Christmas Carols: We Wish You a Merry Christmas
Christmas Classics: Jingle Bells and Joy to The World
I've been practicing only in sight reading, never used the solfeggio pictures.
I can sing the songs in Romanian in the scales I'm practicing on the piano but the kids can't. They are singing in a lower range. The Moon told me that they have short diapason (I'm posting here so we can have a online talk too).
Here are the audio files with the Romanian lyrics or version for each
I have tried to find out how to transpose We Wish You a Merry Christmas to play in harmony. And the comfortable accompaniament for them seemed to be when right hand started from lower Sol. I have also thought an introduction for them, inspired by what my EK sounded when played in Song Bank. I guess I have to find a finish too
But the main thing is:
How do we accompany children singers with these songs? Do we play the right hand (I take this as a focal point, but maybe I'm mistaking) in the scale they sing? Or one scale higher? Or one scale lower?
Even if I won't be able to accompany them correctly and they'd rather use negatives to sing, I would love to hear your answers. It's a great lesson for me.
If you want to know why did I take such a big challenge on myself though I'm at the beginning of beginning... well... I have to keep myself motivated and very preocuppied, otherwise, these months for me, till summer are going to be very tough emotionally and mentally. And playing piano keeps me in high spirits

and that's what I need for the days to come (my husband is on another continent 10 months a year

).