Has anyone used this kind of a swimming mat for their kid? Where can I find it in Singapore?

I read on an online forum that these mats are not allowed to be used in public pools in Singapore as they can be quite a safety hazard. Kids can be trapped under the floating mat underwater if it flips over. May I suggest you try smaller floating foam boards (they resemble tiny surfboards) or arm floaters. They are lighter and smaller -- easier to handle by the kids and less likely to overwhelm them in case of a mishap.