ok first i want to say that i havent had a baby so i probably don't know about anything about when you can start exercising after having a baby but below is my opinion (taking out the fact that you just have a baby). Other ppl who have been through this experience can probably give better advice or i would see your doctor who can tell you if you are ready etc for exercise.
well first of all you cant spot reduce. I would have to say IMHO its one of the cardinal rules of exercise/diet/weight loss. If you lose fat then you lose it from all over your body, thats why the places that you maybe more pre-dispositioned to have more fat (i.e. stomach, hips, butt etc) you will generally lose it last as there is more fat there in the first place - get my drift?? sorry bit hazy...
anyway despite this if you do have trouble spots you can always do exercises to help make them appear more "toned" (i dont really like that word but i couldnt think of anything else). At the very least you will feel better and that you are doing something but dont beat yourself up if it doesnt happen over night....but you will get results in time
people say on here all the time that "great abs are made in the kitchen" (or something to that effect). its so true, eat clean and often with regular intense exercise. I have found that HITT cardio is particularly good for giving a flat stomach and while doing it (and walking) make sure you hold your ab muscles firm (like you have a piece of string pulling your belly button towards your spine) and it will give you a bit of a core workout. By all means though walking is still good but make sure you introduce hills or steps into the mix to keep your body guessing.
I know this is long but i have one more point....
i hate working my abs. I only do it about 1 per week if im lucky twice!!! hehe but i recommend when you do do abs you work your whole core. "upper" and "lower abs", obliques and transverse (?) abs. Pilates is great for the last one!!! I also tend to try to make it interesting by using swiss balls, foam rollers, medicine balls etc.