Oh, I see. So you got a lecture with a handing over of said rules. That does sound a bit harsh, and I can understand why you would take it badly.
To be honest, I know you say they are 'ok' - but the rules sound a bit draconian to me. No chocoalte and sweets at all, and no 'presents' for 4 yr olds at all. Seems quite harsh.
Did your sone give you a reason for these rules?
And has there been any times where some of this has been expressed before?
TBH I don't think it's that bad for parents to request certain things of grandparents, particularly if there is a behavioural problem or specific issues, but I'm leaning towards those who say this is out of order.
Sounds like you need to sit down with your son and talk it through and understand the reason behond the rules and what probelms there are. Initially I would focus on this, as your hurt may be unintentional and you can raise it after understanding.
But some of these I just wouldn't agree to. I might go along with what some of the others have said - a basic message of 'if you want free childcare then I do it my way' but you may well then get the result of them not leaving the kids with you.