Start with Em
Fret the A and D strings at fret 2 with two fingers and strum all six strings gently. Let the child hear each string separately. If one is muffled, check whether a fingertip touches a neighbouring string instead of pressing harder.
Try Am next
Fret D and G at fret 2 and B at fret 1. Strum from the A string and leave out low E. Change slowly between Em and Am. If placing three fingers is still difficult, return to a single-string melody for now.
Which chord is easiest for kids?
Em uses just two fingers and is a good starting point, but every hand differs; do not force a painful shape.