For the sake of accuracy, I've never heard exactly about AK-47 found with elders (I'd assume it's a hyperbole) - but it doesn't change the fact that it could 100% happen in future, and that Russian media is one big lie.
I won't even describe the eyebrow-raising inconsistencies in the official version of what happened in Kerch - I'd just leave this short video here for those who can understand Russian:
https://www.youtube.com/watch?v=31EVB2rBfrQ
For those who don't - one of the main prime time Russian TV propaganda show featured a phone interview with a girl who had been already killed in that terrorist attack.
p.s.: Several days later, to their credit, they found courage to admit (on Instagram) it was a mistake (after it was brought to light by the Internet community), and came up with couple versions of why 'it wasn't their fault' :)
P. P. S: just look at the 'grieving' president of a country that has sacrificed lives of tens of thousands people to get control over Crimea (where Kerch is) the next day after the terrorist attack:
https://youtu.be/NKRKDxSn5i8?t=21
He says "I'd like to wrap up the discussion, since I'd like to play hockey on my way to Uzbekistan"
I guess there is nothing to add here...