I'm lucky to have a youngster right now, he's adorable! It's good to put the crickets in a plastic cup, one of those party cups ment for ruit. Then sprinkle a small pinch onto the crickets, and place another plastic party cup ontop. I love how they remain .33 of an inch above the cup. It provides the crickets the perfect amount of space, allowing them to be moved around in for dusting purposes. Then I'd tilt the cup over against the screen, the crickets climb upwards. In my experience, it's easier for the little guys to catch with clear view of their prey, rather than go looking in the plant and on the bottom of the cage.
I got him cup trained. It didn't take too long, surprisingly, considering his age. At first, I place a few little Superworm cups you find at Pet Co., with a few crickets in each. I like to show him that theres crickets in it, so I place them on the bottom of his cage, with a couple bio vines a few inches above. It's good to have them a few inches above those small cups, so he has a longer distance for his tongue to reach.
Whenever I place crickets in such a shallow container, I let them go in it from releasing them out of the party cup. I hold the cup over the container for 7-10 seconds. They don't jump out if you do that. It sounds stupid, atleast I think it does lol. But it works for me!
Why do you feel your little one isn't getting enough Cal.?
Try not to mist his/her cage while the crickets are free ranged. The crickets might get sprayed too much and the supp. might get washed off.
If you decide to cup train, it's much easier keeping the plants a little wet.