There's an entire baby related section on the sq website. You may want to check it out? But from what I know, travelling from Singapore to any other country, as long as the total amount of bm is in the weight limit, it's okay. But from shanghai to singapore, with different custom and aviation rulings, you might want to get a confirmation from the station manager posted in Shanghai.
https://www.singaporeair.com/en_UK/us/faqCategory/?category=29961#question-34753
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