Strangers picking your children up!

This is just something that I can't stop thinking about, had to post about it.

So today me and my partner took my nearly 1 year old son to a museum today along with his 3 year old cousin (girl) and parents.

Whilst the other 3 adults where near the exit looking at something I was following both kids walking around, ( there was maby 2 other people there so I wasn't worried about them getting lost, as we got to the back my son turned round and was only a few paces ahead of me and a man ,maby in his 40s picked him up, he had 2 other Male friends who didn't say anything just stood looking at exhibitions, anyway he didn't say anything offensive,was being nice but I got him back and just as I did he held his arms out and picked up my niece,literally for a few seconds and put her down, I grabbed her hand and took her back to her parents,who then told her not to let strangers pick her up.

I just think it's so scary that it's so easy for random people to pick up kids they dont know, and how my niece just let a complete stranger pick her up. I know it could of been completely inosent, but I just keep thinking about it. I'm definitely not okay with complete strangers holding my son.

How do others feel on this? Has this happened to you?

I will be nervous now getting him out of his pram.