Unless you are a superwoman from a far away planet, the mere physical fact you carried two babies to full term, means that to do so you had to have had an extreme stretching of your anterior abdominal wall.
That means that to allow your uterus to expand with the growing babies, your six pack (rectus) muscles were stretched AND pulled apart sideways from one another, some laxity between the side muscles (ie the transversus abdominis, internal and external obliques and the six pack muscles has occurred and your skin was stretched out. moreover in many cases the pubic mound (mons pubis) drooped, the breasts deflated etc.
As you well know, cooking a piece of steak is associated with significant shrinkage. The heat shortens collagen bundles. Many current technologies purport to shrink skin by warming / heating it. But - EVEN IF such technologies were always safe in all hands and worked reliably in every patient - which they do not - such technologies will not put the underlying loose muscles back togerther again and you will be left with a disappointing result and a lighter wallet.
If you are done having your children and want to look great, I would suggest you find a Plastic surgeon in your area who enjoys performing Mommy Make Over procedures and have him/her give you a great tummy tuck. You will NOT regret it!