You need to ask the shop concerned what size they want them at. They will need them to be at a saleable size usually, so about the size yours were when you bought them, maybe a tad smaller. They should be sexable by the time they are around 1.5 inches SL.
I sympathise: watching them breed and raise babies is wonderful, but letting the youngsters go is always a bit sad
The last spawn from my panduros was huge and though I've sold some privately I have about 30 still to move on as I stopped advertising them in the cold weather. I'm taking some of them to the BCA auction next month, along with the last of my Angels' babies (who are about 4 inches now) as they are not getting on with Mum and Dad, and a 5 inch male Rotkeil Severum and 2 Julidochromis transcriptus who were all left over after the others in their tanks paired up.