Hello Yogamum! Congratulations!
You can use Mooladhara and Uddiyana Bandhas to strengthen the pelvic floor and diaphragm.
Poses that may help:
To strengthen back-
Locust
Bhujangasana
Yoga sit ups and reverse sit ups
Cat/Cow
Ardha Matsyendrasana (1/2 lord of the fishes)
Ardha Mukha Svanasana (Down dog)
Abdominal strengthening-
Navasana
Modified Chatturanga, with knees bent and ankle crossed
Dolphin
Setu Bandha Sarvangasana
Urdhva Dhanurasana
Paschimottanasana
Jathara Parivartanasana (supine twist)
Uttanpadasana (raised leg pose. On back, knees bent, lift one leg toward ceiling)
Supta Hasta Padanguhtasana (reclined hand to big toe w/ leg out to side)
I have listed these in no set sequence. As you have practiced for 7 years, you can probably place these within your own home practice. Take it slow and easy as you return to your practice. Be mindful of what your body is telling you.
Hope these are of some help to you! Best of luck and enjoy this special time with your children!