I'll prefix my comments with a link from teh Tips section mainly since I suspect you may have made a few of the same errors I did.
Pregnancy/Maternity and Photography – Gerrys Tips and tricksI think you may have had the subjects a bit too close to the backdrop, now I know you are/were limited by you sheet size but I think its probably a good aspect to address sooner rather than later, i would also suggest any natural BG around you house/garden may also serve well too.
In teh first image the BG is a bit distracting, possibly blurring it out slightly in PP may help,the pose in this one is classic and I like it, possibly getting her face titling up and towards teh camera fraction more (whilst still looking down) may have been more flattering. The hand position could also be improved by lowering them slightly so that the hands are cradling (more from underneath), this would also use the arms to cover more of her lower skin thus not 'cutting' her midriff in half so to speak.
The second one, i reckon the ladys hands could be cradling rather than 'hands on hips' since that gives (to me) a bit of a stand-offish attitude whilst the dad (i assume you) is closely engaged.
I actually don't mind the last one, the pose and teh heart shape is cool - the selective colouring is fine imo, however its a love or hate thing in most peoples books.
In all of teh images I think a bit of further work on the BW conversion would be beneficial, gettign those greys out of there are getting some nice Blacks would be more appealing to me.
With regard to your lighting, don't be afraid to add some shadows to give teh images some more depth - i am sure others here with more lighting experience can give more/better suggestions.
hth and I look forward to the next set.