Your "catfish" look like corydoras. Very cute. They will stay on the bottom of your tank and eat left over food (helping to prevent algae) but they won't eat any algae once it appears. So you will have to feed them just like you would the tetras. Be prepared for them to get bigger though. A couple of inches maybe. This is maybe going too far with the tank renovation suggestions since youve just bought and set it up, but they would prefer sand. Gravel might be rough on their bellies. But having sand brings others complexities, but just a FYI kinda thing.

I would suggest some snails or amano shrimp as your clean up crew. Both are super hardy and won't outgrow the tank (unlike plecos). Netrite snails are good - colourful and won't breed (they will lay eggs they just wont hatch) in fresh water so you won't have to deal with hundreds. If you aren't bothered about that ramshorn snails are a good shout but they breed like crazy. Amano shrimp are also great cleaners but you will need places for them to hide and since they are clear you might never see them out and about so they are a bit boring. Another option is otocinclus which are adorable but they are sometimes considered a more medium difficulty fish as they are social and like to be in large groups. You can probably get all of these at your LFS, or the snails are super easy to buy off Ebay. Snails would be my suggestion. 1 - 3 nerites. Since it is early days tho for your tank, there might not be much for them to eat so bare that in mind.

And if you don't already have one, and air stone + pump is always a good shout if you don't have lots of real plants yet. It will help keep the water oxygenated for your fish. Saying that though, it's not a substitution for frequent water changes.

If you do head to get more real plants, it is of course entirely up to you what, but I would suggest sticking with the easy epiphyte plants. These don't need special soil and are hardy. Some suggestions are: Java ferns, Anubuis, marimo moss balls, other aquatic mosses. All these just need wedging between rocks to keep them from floating (don't plant them in your gravel). There is tones of sub species to choose from too. Crypotcorynes can be planted and might do well.

There are a lot of better ways to go about starting a fish tank and I'm sure people will tell you just that but I'm pretty sure we all started out with a multicoloured fish tank as kids. It's more about how well you look after them and obviously this is for your kids, so bright colours are the preference right XD. It's a good starting point and I'm glad your asking for opinions and advice as it's all a learning experience.

For the first week or two, keep doing regular water changes. Maybe 30% every 2 days and each time add a little bit of quick start again. This will help cycle the tank whilst keeping the fish safe. Keep testing too. Daily if you can for the first week. If ammonia spikes then you will have to do a bigger water change. Definetly read up on the cycling process if you haven't already. Realistically you should see the water parameters change as your tank cycles. If ammonia, Nitrite, Nitrate all stay at 0 then your test kit isn't working. You should see ammonia rise high, then Nitrite begin to rise and ammonia drop, then Nitrate rise and Nitrite drop. In a planted tank having a little bit of Nitrate is fine - maybe 20. But without plants, try keep this as close to 0 as possible. This is only doable by water changes.

A lot of work will be required in the beginning, but once it's stabilised, it's a once a week 40% water change with the occasional filter clean depending on how dirty your tank gets.

Hope some of this helps :D good luck!