Let's just say your son's friend is turning 8. Invitations to the party went out several weeks ago. Less than a week before the party, his dad sends a (unprompted) message to the parents of the invitees saying we already have enough stuff so please no presents, just cash if you'd like to give a gift. Many of the parents will have already purchased a present, given the short amount of time until the party.
Not sure if relevant but I should add: the family are minted and many of the invitees are not.
Are they being unreasonable?