Aiyooo I totally get it, celah peha kan memang gelap naturally sebab area tu terlindung dari matahari! A few of us mums tried exfoliating gently dengan body scrub 2-3 times a week, then moisturise heavily dengan kaya cream or body lotion yang bagus, consistency is key lah, kena buat habit. Some of my mum friends swear by using vitamin C serum on those areas (the same ones for face boleh juga) sebab it helps with brightening, then seal with a good moisturiser. Another trick, avoid tight pants or chafing so the skin can heal better and look cleaner, sebab sometimes the darkness is also from irritation.