Negligence in Safekeeping

Hello and blessings.
We were on an outing with the extended family,
My relative went into the water with her small son and asked me, since I was outside, to put his kippah into some bag. I took it and passed it to someone else who was near the bag, and asked her to push the kippah into it. I saw that the bag was open, but I thought it would not fall out, and at most it would be next to the bag and they would take it when they came out. In practice—the kippah was not found....
Am I obligated to reimburse the value of the kippah because perhaps I was negligent and did not watch it as required?
Thank you very much!!!

Hello and blessings 

You are exempt. 

They did not ask you to guard it, but rather to place it in a specific place.