I think you may also need to find a better treat. At the moment, it doesn't sound like they're excited about whatever you're giving. It's a bit like giving someone who doesn't like chocolate a box of fancy truffles - you think that they should love it, but they don't!
Try offering a plate with different treat items on it, and see what they go for first. You might offer hulled sunflower seeds, pieces of flaked almond, small pieces of walnut, pinenuts, little bits of dried banana chip (make sure it's sulphur-free and contains no added sugar or honey), millet and so on. I personally use flaked almonds - they're easy to break into bite-sized pieces and can be obtained from the bakery aisle at a supermarket.