i agree with above ^ Finding out if you or your kids will take care of them would help, but if there younger then 10 ¬¬; most likly you will be the care takers. I watched my niese move off of taking care of the fish after awhile and I had to tell her mom and she ended up being the parent to the fish. But a snail is questionable.. if it's pregnant you'll end up needing to get rid of a whole tank load of em.. My mom had to stop taking care of fish cause her tank was emptied from all of them and the fish, and then the fish where put back in and the Snail eggs that we couldint see. Hatched! so a week laiter we threw the whole tank away.. it was a real waist and and being a kid myself at the time it destroyed me for 12 years form fishie lovin'.
It can fit alot of fish O_O! From a few guppies to at least three female bettas.. But not together of cource ^^; hm... Well I know for sure that you can fit 7 guppies or 5-7 tetras,3 female bettas, a mix of Tetras guppies and algie eaters ( about 6-7 fish.
Like many people say"
" One gallon of water to every one inch of fish"
But for Bettas I like to see females in threes at a friends house, and she has a 6 gallon. so that kinda helps in solving them. But it sounds like you could get a little more exotic for you kids =3 and knowing them they would love this one..
How about, Two algie eaters,three swordies and a goldie? Kids normaly go for gold fish inless there super informed on other fish, and if I was a kid I would have had Bettas gallor when my mom had her 50 gal XD. Sometimes it's always best to ask the kids what they want =3 take them to a store or show them a web site with all sorts of fresh waters, or salt if your willing to take car of the expenses. Then see what catch their intrests and be sure to tell them that they can pick two fishies each=3 that way when they end up picking a fish that needs a school of it's own kind like guppy or tetra, you can get more then a few of them. And if they pick different Tetra or Guppie species, you can get alot of them ^_^.
but it all depends, researching on your own favorite fish would help out, but you could possably also show them fish you like and see if they also like it. Many times kids like what they dont have. So if you show them a bunch of fish you like. They will most likly love it! ^^ hope this helps. Just be sure that if it is a 5 gallon, get five fish small fish or 3 medium fish or one big fish, if it's a 7 gallon get 7 three small fish and let the kids watch them breed for expeariance and fun to you and them as the babies mature. or just 7 small fish or 3 medium fish or one big and one medium. And also when your just starting with a big tank like 5-7 gals.. =3 getting a small algie eater is a must ^^; thats alot stuff for a 7 gal so having a acomplis like a algie eater to help in keeping it clean with the filter would be a great match. And the kids will go crasy when the thing sucks onto the side of the aquarium and shows it's "fangies" lol XD I loved my moms algie eater!! And I was only 5.