While lots of keepers here and even breeders (here in Australia) advocate using dry screened playsand even for the very smallest and youngest ,even just hatched bearded dragons, there is a strong risk of the little dragon ingesting some sand when eating and this can prove fatal if they become impacted.
BEST NOT USE ANY indigestible particulate beddings for young bearded dragons (this includes play sand) and definitely do not use CALCI-SAND (it's lethal and turns into concrete in their guts).
As already advised, I also STRONGLY ADVISE you remove the sand IMMEDIATELY.
If he has been eating sand you will need to watch his pooing and how regular he is for at least 2 to 4 days (it can take this long for anything that goes in their mouth to come out the other end).
Make sure he's very well
hydrated and maybe give him 0.1 - 0.2ml of olive oil by mouth each day to help lubricate his internal plumbing.