I don't see how a tongue would be inferred. There has to be a bottom lip in that expression: if a tongue was extended, a border of a bottom lip would still be visible underneath. IMO, I wouldn't do any kind of retouching of the lip's border because that's the natural skin tones of the mother. Although if you were going to work on that area....perhaps brightening and adding some more saturation to her lip (to further separate). With the picture as a whole...is this the whole frame, or can you crop a bit further down? I might try bringing out their expression by having some induced vignetting in the corners, as well as softening in corners/sharpness in the center.