Hello KaZ38
If they are only eating the flakes that fall down it probably means they are a bit scared to come to the top for a couple of reasons. Little fish are usually more willing to come to the top when there are plants that go all the way to the top too. You could put some twisted val in the background that will eventually twist over the top surface, or some ambulia, cabomba, stargrass - any stem plant really.
Many little fish also only feel safe in a larger group so it might improve straight away if you double them.
The other thing you can do is go to the chemist and get a dropper (I use the one with the pink rubber squeezy bit), put some flake in some water from the fishtank, then suck them up and fire them into the water towards them (similar to GrahamC's suggestion). Some fish like to think their food is alive and it helps when it's in the water rather than floating.