You have to be very careful with kiddie pools, they are very slippery so it can make it very hard for a duck ( Especially a heavyweight breed) to get out, I'm assuming your Pekin was done swimming and tried to get out to no avail, and ended up just floating on the water and started to get chilled, I like to add rocks into the pool, or a ramp with hardware cloth attached for good traction.
[/
Also, what is your set-up for ducks getting in and out of the pond? Even now that my ducks are grown I have concrete blocks inside the pool that come just a few inches short of the top rim that they stand on when they want to get out. Then I have a ramp going out of the pool that is almost two feet wide, which they can easily walk down. However when they were babies like yours, they would often fall off the sides, so I blocked the sides - they are clumsy and it's up to us to protect them
View attachment 2108209. Make sure you have a good set up for getting in and out.
Thanks for replying and I will definitely be taking your advice on the pool issue. He is back to his old self this morning. When I picked him up he went to biting my ear which he has done since the first day I got him. Thanks again