As stated, Koi
should be in ponds, or very very large aquariums when small. They can reach 3 feet in length, and poop a lot.
The "suckerfish" can be anything from a Pleco to an SAE. Will most likely have to be rehomed if it is of a common specie.
The Barbs will also get very big; up to 16 inches!
I would suggest rehoming all of your fish, as they will get too big for your tank.
Now, your tank is appromixatley 8.4 gallons. If you want something colorful, you could dedicate your tank to a specie-only tank with Cardinal Tetras or Neon Tetras (I personally like Cards). You could get by with 8-10 Cards if you are good with water changes. Live plants would look very good provided your lighting is not indancascent. I am going to use this setup in my 5 gallon.
Mollies will easily overrun your tank. They are livebearers and will produce almot every 30 days if a female has been exposed to a male.
How about you take your kids to your local fish store, and see what they like. Write the names down. Then, come back here and post the names, and we could figure out what they like best.