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That one turned out quite nice. The lighting is quite nice.
What you did, perhaps without realizing it, was to keeop the angle of the flash on the reclining face more or less similar to the angle that winds up looking most "normal" in an upright shot.
It's a perceptual quirk, but when looking at faces in photos our brains try to match the contrast pattern created by the lighting to the mental image of a face seen in "normal" lighting in the full upright position, like this...
Rotated 90° you may find the face easier to relate to than when seen horizontal (I find that is true for myself). Rotating the face into the orientation they are normally seen also makes it easier to objectively evaluate how well the key light angle to the face modeled it's natural shape. Quite nicely here, but you'll note in this vertical view the angle of the key light is slightly below the eye line. Even in the horizontal view if you positioned the key light over top of the head you'd wind up with more natural modeling, per the mental baseline of what a face normally looks like in natural light when upright. Try both ways next time and compare you'll see what I mean.
The mental image pattern of a face is one lit from above with the key light 45°V over the head relative the eye line, then either "noon day" centered in the nose vertically (for full face views) or 45° H to the side of the nose for oblique views like yours. If you use the 45°V0°H "butterfly" strategy for full face views and the 45°V45°H "short" strategy for oblique views of faces the net result will always wind up looking naturally 3D and flattering because that's the angle of natural lighting that forms our perceptual baseline for what seems "normal".
In terms of posing, propping a baby at angle with pillows or couch cushions covered with a sheet will make it easier for the viewer to relate to the faces. For example here's one rotated to 45° which is a happy medium between vertical and horizontal.
As for light vs dark backgrounds? On a black background when there is a lot of negative space it tends to create a "baby floating in space" look. Shooting on white backgrounds creates a softer overall look I find more in context with infants. You also get bounced fill to open the shadows for a softer look. The choice of plain clothing was a good one as patterned outfits while cute in person tend to become distractions in photos. Keep stage lighting in mind when holistically looking at the contrast of face, hands, feet and clothing. Decide which is the "star" on that particular shot and put it in the "spotlight" (i.e. the brightest part of the key light). Choose clothing and background with that in mind too — find combinations of clothing / background / lighting that make the front of the face contrast the most and it will automatically become the star in the "spotlight" which attracts and holds attention.