There are also some more colorful schooling fish that you could add right away with the Bio-Spira. Some examples are: Lemon tetras, Harlequin Rasboras, Head and Tailight tetras, Flame tetras, black neons, and glowlights.
Danios are alright, if thats what you like, but personally I like a little more color (and your kids might also).
Pick one type and get about 6 to start with when you add the Bio-Spira. Then a week later add another schooling type, a gourami, or cories. Then a week later add something else.
In my 29g tank, I have:
7 neons
7 glowlights
1 opaline gourami
6 panda cories
3 ottos
I am kind of bored with the neons and glowlights, but I chose them so I have to keep them. My 29g is heavily planted. The neons and glowlights are very colorful.