First in C major, then in D major, then in C major, then in D major.
It is impossible to expect ordinary children to sing well. If you have a CD, just sing along.
So don't rehearse too much.
Beginning part:
The first paragraph of key c:
3 4 56 5 -| 12 34 3-| 55 6 1 1 5 | 5 32 2-|
34 56 5-| 12 34 3 -| 32 1 1 1- | 6 3 32 1 1|
6 5434 | 34 56 5| 34555 5 127 6|
65434 |32354 |3455-|5 36 65-|
Turn the second paragraph to d:
3 2 34 565 |3234565 |56776 |34565|345454 43 12 |
3234565|3234565|566776|345565|3454 43 12 2 1 1|
bowstring
The first paragraph:
C - | C - | C - | G -
C - | C - |C - |Am-C-|
F - |G - |C - |Am - |
F - |G - |C - |F - |
The second paragraph:
D - |D - |G-Bm-|G-A-|
D - |D - |G-Bm-|G-A-|D -
There may be some inaccuracies. But that's basically it.