Advising extending family members that we do not celebrate birthdays

As Salaamu Alaykum,

As parents we work towards teaching our children the correct Islamic values and do not encourage or celebrate any birthdays and have notified our extended family members. However, the extended family members do celebrate their birthdays and also continue to wish our children on their “birthday”. Should we remain silent when it comes to them wishing our children or is it permissible to notify them (elders included) that what they are doing is incorrect. What is the best way of notifying them without coming across as disrespectful or rude?

Shukrun