I bought this one size up based on other reviews. My son is 5 years old and weighs 38 kg. I bought the small size and it fits my son very well. He's a bit skinny so this shirt isn't too tight for him, but I wasn't expecting that. I only bought one because I wanted to test it for both pajama shirts and gaming and I will be buying more for both purposes. This is a great basic shirt that is great for many different functions.
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