first and last picture seem to be 77mm TOX ammunition of German origin.
Dug up a 60Pdr TOX with Nr44 fuse yesterday...
It's normal habit for farmers to put shells in lamp posts, as that's about the only place they aren't in their way on/aside the fields.
Contrary to what everyone thinks, ammunition is not collected on a regular basis by EOD.
Procedure is as follows: ammunition is found, police is informed (and show up a couple of days later, as ammunition is a daily occurance over here).
The police then informs the EOD that on that spot ammunition is found and has to be taken away.
According to the size and spot where found, EOD decides if it's urgent or routine.
If urgent, it get's taken away on the day itself.
If routine, it get's taken away when a team passes near that spot (can take from a couple of days, to a couple of weeks).
EOD will NEVER take a shell with them that is not accounted for. So if they don't have the paperwork to take it, it remains where it is.
I personally know of shells that are laying next to fields for many years now. EOD knows where they are, but the farmer can't be bothered to inform the police.
So if no police comes to do the initial report, EOD doesn't take the shells.
As for kids: I have known these things laying about the place for as long as I can remember

And my kids are taught the same by me, as I was by my great-grandfater: leave ammunition where it is. There's plenty of other stuff on the fields that are worth collecting.
Hope this sheds a light to the EOD procedure, and why a lot of shell keep stuck in a Belgian lamp post