A couple of thoughts.
1. If you're breastfeeding, your body will hold only some extra weight to keep up your milk production. Especially with your second child.
2. Be sure you're eating enough. I went off the deep end with clean eating and calorie reduction after having my second a few weeks ago. I noticed that once I boosted my calories every few days, the weight just fell off and I got my shape back much faster. I'm 11 weeks post partum now and back to normal.
3. What does your body respond to fitness wise? For me, it's circuit work, so I've done a few different rotations lasting 4-5 weeks. (I started working out 1 week pp).
4. Don't focus on your weight. Focus on your shape and how your clothes fit.
5. Hit your abs HARD, daily. You can do this while playing with the baby, standing upright (pull up on your abs, belly button to your spine), giving your other kiddo a bath, etc... Planks are your best friend right now. Your transverse is what gets totally blown during pregnancy, and it's the muscle that will pull everything back flat for you again the fastest. Crunches won't be very helpful until you have your transverse strength back.
And patience, of course. I've had to remind myself that 1000 times, and I'm finally back to normal now after weeks of panicking that I'd lost my shape forever. You'll get there. Just give your body time to respond.