Baby Sebamed 50+ Sunscreen Failed to Protect My Children

I bought Baby Sebamed 50+ high protection sunscreen and applied it generously to my children because I didn’t want them to get sunburned. The cream was thick and left their skin very white, but despite this, on the very first day of our vacation, my children, who only went into the pool, ended up with dark tans. How could this happen with a high-protection sunscreen? I’ve always trusted Sebamed for baby shampoo, oils, and other products, but I regret using their sunscreen.