Here's my version with a dotted eighth note on the 3rd beat of the first measure and triplets on merrily. Somehow though, the merrily sounds rushed. We did sing it in a round that way didn't we? (You can hear it at concertina.net)

X:1
T:Row, Row, Row Your Boat
M:4/4
L:1/4
K:c
CCC3/4D//E| E3/4D//E3/4F//G2 |
w:Row, row, row your boat, gent-ly down the stream,
(3c/c/c/ (3G/G/G/ (3E/E/E/ (3C/C/C/| G3/4F//E3/4D// | C2z2 ||
w:mer-ri-ly, mer-ri-ly, mer-ri-ly, mer-ri-ly, life is but a dream.