If you want maximum health, I would suggest planting them straight into the ground since moso seems to hate being in pots, but of course preparing the soil beforehand. If you are in a suitable climate, you can probably expect shoots to get up to 2-3ft the first year, and they may get up to 7ft next year if you are zone 9 with ideal conditions.

Here's a picture comparing how dark the seedlings that have been in the ground several months are compared to the newly planted ones. They simply hate being in pots.

Here is a link that might be useful:

Only one has survived, but it has not grown an inch. Six months later and it is still the same size. Curious.

Young Moso does not like full sun. Too much water is a problem for me when I keep them in small pots.

A larger pot is easier to get growth from, by my experience.

Also, they may not grow much above ground for a few months but the underground roots/rhizomes will be growing if conditions are right, and as long as it looks healthy, then just be patient.

Kt

It looks like your potting mix may have some kind of nutrient deficiency, and if they haven't started shooting after a couple months of germination, there is definitely something wrong. Someone on the bambooweb forums with the name Tarzanus claims to know the required nutrient, but I've happened to never have problems after growing hundreds of moso seedlings with my home-made potting soil.

You might want to just go ahead an ask someone on bambooweb for a moso division because it is a pretty common bamboo. Mature divisions are much less picky on what they require for soil conditions. Here's a blog with pictures on how I treat my moso bicolor, a variagated kind which is a bit less common, but will also be widely available in a few years.

Here is a link that might be useful: My moso bicolor and how it's treated