A good number of orchids came as 2" inch baggies from Lowes/HD...they are fun - you have to wait a bit, but the flowers are so rewarding (after the wait), and the variety of different hybrids is great...
I treat baby catts a bit different - finer mix. Some - I put in straight sphagnum, but then, importantly, in clay pots. Pure sphag works great for me (I am sure there will be critics to that, but hey - it works, plants seem to grow fast and the roots are beautiful...) After they've overgrown 4 inch pots, they go into whatever regular catt mix I use :)

Olya

Keep catt seedlings warmer than regular catts at night (60F minimum) and give them slightly less light than the adults until they grow a few more p-bulbs. Olya is right about a finer mixer and spag works great in a warm Florida or Texas climate.

I got a new baby cattleya I hope it grows

I feel use the same potting material as you would for a large plant. Bright no direct sun until they get some roots and size. Then increase the sun. A little extra water. Root stimulator is good. I use maxi-crop.