Honestly, it's worth waiting until your body is ready, most advice points to at least a month after delivery before starting any proper exercise, longer if you had a C-section, so don't rush yourself. My neighbour brought her baby along to a postnatal Pilates class that uses the babies, hand weights, and Pilates balls to work on the core and tummy area, and she said it was fun because the little one was right there with her. There are also "Mums, Bums and Tums" style postnatal classes running on weekday mornings that are specifically designed for postpartum mums, which sounds more targeted than just jumping back into a regular gym class. Some mums swear by Pure Fitness for a more structured gym environment once cleared by their doctor, though a few found it harder to stay consistent without that postnatal-specific support. My lean would be to start with a dedicated postnatal class first to rebuild core strength safely, then layer in more general fitness once you feel stronger, the 11 kg difference is very manageable, just give it a bit of time!
How old is your younger one now? Exclusive breast feeding helps in loosing weight. Actually for personalized, medically approved weight management post-delivery visit specialist centers like the Singapore Sport and Exercise Medicine Centre (SSMC@KKH) for an individualised exercise program Below is the link https://www.kkh.com.sg/our-specialties/womens-services/ssmc-women