First, you need to make the suggestion to your kids or grandkids as to what they can do for their dad on father's day to make it special and unique.  Show them that their gift must result in something unique that  dad doesn't expect or would treasure unlike many store gifts.

And here are some ideas.  You could have younger kids purchase a scrapbook and some picture corners.  Then you can put together some pictures of the family, some scrapbook "ingredients", some other art, paint, crayons, etc...  Let the kids' imagination
go wild with creating the perfect 'my life with daddy' scrapbook gift.

A scrapbook obviously won't work with older kids so let them make some chore coupons to do things dad usually does such as take out the trash, mow the yard or whatever else they can come up with.  Dad will certainly appreciate this type of gift.

If you kids want to purchase something special from the store, at the least make them pay for it out of their own money. It is also a good idea to let them personally pick the gift.  If they do not have any saved money, you can also let them pay you back by doing chores around the house.