My very healthy, but Down's Syndrome, 9 month old nephew was visiting. His mom treated him like he was "going to break" all the time, like he was delicate and fragile like a piece of glass. I suggested she instead treat him as she did her other child, only even moreso. (Like working with PT to strengthen his limbs his breathing, etc. rather than keeping him at home, in a car seat or stroller all the time). We all went to the pool. I, the eternal optimist. insisted the kid be hauled into the children's pool with all our other children. He LOVED the water, kicking and splashing everywhere....BUT after about 30 minutes, he deveolped a vivid Harlequin's Sign! We couldn't miss it! One half of him was pale pink, and one half of him was CYANOTIC BLUE! Of course, we hauled his cute little butt out of the water, and warmed him up pronto! I am NOT a peds nurse, but I had her get him to a cardiologist within the week...Yup, sure enough, he had cardiac defects that had been overlooked to that point! He since has had two major surgeries and is doing well.
We tease each other that either I nearly killed the kid by freezing him in the pool OR I saved his life by noticing the Harlequin's Sign and getting him to a proper cardiologist.