Thank you for your question. I agree with other plastic surgeons that if you plan to have more children you should wait until you're done having children before you consider having a tummy tuck.
However liposuction, and in particular laser liposuction, can remove excess fat and also help tighten the skin of your abdomen. Since you are working hard at exercising and losing weight but still have excess fat I think laser liposuction is an acceptable alternative to a tummy tuck since you are planning on having more children.
If you do choose to have liposuction and become pregnant again just work hard to avoid excessive weight loss during your pregnancy.
Be sure to consult a plastic surgeon who is certified by the American Board of Plastic Surgery, experienced in body contouring procedures, and who has an excellent reputation in your community.