tell your son congrats, the army looks awesome, and the scuttlefex looks badass, reminds me of the bugs from starship troopers.
I'd love to see some more close up shots of each unit. so perhaps take a few of each group/type for us

Assuming he paints them? is he looking for tips?
Currently
id recommend getting some basing done, models go from being good to great with a good base
imo. His skin technique is really nice and excellent for a 9 year old, i'd recommend some washes to go along side his armour and blade colour choices.
Also something fun he might enjoy;
Get him some Uhu glue and tamiya red clear ink.... then do this;
Its a very simple technique, its also really fun and highlights how nasty his nids are. Or another take is to use a green ink and do a slime effect
Keep up the awesome work and look forward to seeing some more.