You've got some nice natural backlighting, so you need add light to the front of your subjects. Even mounted on the hotshoe, your SB900 would've been a great asset on these. She looks dull in comparison to the scene.
It looks odd that the child is not pointing towards the baby bump.
The last shot is a good idea, but as is, it is not so good IMO. The horizon is tilted clockwise to the right. That can be fixed. However, the subjects are also heavily weighing the image on the right. A better balance would be to have the child shift to his right so that he is positioned to maybe where mom's knee is raised. You can then move to your left or right slightly to nail the perfect frame.
Lastly, I think more interaction would help. There is only one photo where she is looking at the camera.
Not too bad for a first time. Thanks for sharing.