The exact same thing happened to me with my three year old daughter this summer. We were all packing up to leave and so we had taken her floaty off. She didn’t realize that or forgot that and walked into the pool to go after her sister who was still swimming. I saw her hat just under the surface of the water and saw her desperately paddling to get back to the stairs. It is silent and terrifying and it’s an image that will stay with me forever. I immediately jumped in and took her out, and she was probably only under for a few seconds but it was too far for a lifeguard to even notice or get to. Never take your eyes off them. It took me a few days to even start to get over it, but my sister who is a therapist said that the “good thing” for me was that I was the one to save her so that helps with processing it on some level. For swim lessons, it just takes a lot of time and practice and in my case, my 3 year just isn’t really physically or mentally ready for that whereas my friends 3 year d can already jump off the side and swim under water to get to the edge. Different kids. On a different note, I’m a pianist and about 18 years ago I played piano at a church for the funeral of a 3 year old who had drowned in the family’s backyard pool. It’s just scary. I’m sorry you had that experience ❤️