The only reason I wasn't suggesting a single larger fish like a betta or gourami is that many of my customers who bought biorbs were NOT happy with the idea of a single-fish aquarium (I can't print most of their comments on a family website).
I don't think the flow in a biorb would bother any of the common bettas or gourami's.
However - right now I would avoid "dwarf" gourami's, as there is a virus going around most of the dwarf gourami wholesale population from SE Asia and they are not in good shape.
The only downside I see to tetras is that if you cycle traditionally (ie slowly without any "boosters") you really can't add a full school at once to such a small tank - just 2 (maybe 3) fish at first, then 2 or 3 more after a few months, etc. Which can lead to skittish fish.
However - adding a booster like Stability (from Seachem) or Safestart (Tetra) can make it easier to add more fish sooner. But I'd probably plan on eventually having a single school of one species, rather than a noah's ark of 2 of this and 2 of that, if your going with tetras.
Skipton's had a pretty good mix the last time I was there, but I was out sick this weekend so I'm not sure for certain what's in stock.
Off the top of my head:
Cardinal Tetras
Black Neon Tetras
Silvertip Tetras
Rummynose Tetras (kinda delicate to cycle with)
Red-tail Blue Columbian tetras (too big)
Ember Tetras (my first choice - bright red and peaceful)
Von Rio Tetras
Blue Tetras
Redeye Tetras
Pristilla and gold Pristilla tetras
Congo Tetras (too big)
Head-and-Taillight tetras
Splashing Tetras
probably lots more I'm forgetting...
other small fishes in stock:
Danios
Celestial Pearl Danios
Harlequin rasboras
a few really nice "micro" rasboras including
Boraras merah :

Emerald Eye rasbora (
Rasbora dorsiocellata)
Norman's Lampeye (
Aplocheilichthys normani)
Pygmy Gouramis
And probably a few more fish I'm forgetting.
I think the micro rasboras are small enough that you could keep 2 small schools, but they may be too small for a young child to enjoy.
Another option - add a little crushed coral gravel, add a little pH buffer to the water, place a few snail shells on the bottom, and put in a pair or trio of small shell dwelling cichlids.
As long as you kept up with the water changes, multi's would probably do fine in there.

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Rich
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