We can learn a lot by listening to SONGS we learn on the cello being SUNG by SINGERS! Everything we play is not a song... but those things meant to be sung are songs, and we should likewise sing them on our cellos. Here is one example of a song we learn at the beginning of Suzuki book 3.
We know it by the French, "Berceuse". "Wiegenlied" (VEE-gun-leed) is the German word for lullaby.
Here is one example of how it is sung - maybe when the baby you're singing to is at the back of the cathedral? :-)
You might like to look up examples of other singers as well.
This is the best cello video I found with the arrangement we play. What does she do to "sing" with her cello?