hey, I have two toung children- one just 4 and one just 2. I breast fed both, so first of all, some advice with that: Be careful working out b-4 feeding, it makes your milk bitter. Also watch your diet, baby NEEDS that fat! If you are not breast feeding, disreguard.
As for what to do, yes, you can burn fat by doing weights and moderating diet, but getting your heart to a healthy place is a good way to start. Do some cardio and see how high it goes and how long it takes to recover. If you stay in the 120s or so no sweat, jump to weights. If you're up over 150 and take some time comming down, do some cardio every day- 45 mins is good and then do a different muscle group every day for the remaining 15 minuts- keep in mind you can do more weights if you do some at home. Bench your baby too! His weight will increase as you become stronger- it's perfect
Of corse, alternating works too- but be careful of lifting too much, because your muscles are probably still loose from your pregnancy- they stay that way for about 6 months or so, so start slow to avoid injury. If you are already lifting lots, no worries, just be careful!
Hope I don't seem like a know-it-all... this worked for me and is my opinion (based on one avenue of thought).