Blooms and cloudiness are extremely common in newly set up tanks and can sometimes take quite a while to clear. In my experience they are nearly always a non-issue and beginners worry disproportionately about them. Believe it or not sometimes the chemicals that cure out of the silicon sealants are a favorite munch-down for the heterotrophic bacteria and that is often the initial bloom you see. I also think there is something about the way some modern water treatment systems handle the water that can leave a multi-day lingering cloudiness - I've been seeing that sometimes after my own water changes even though it is a mature tank.
Don't be distracted by your cloudiness. Keep your eye on the big picture, the all-important initial weeks and months you have in the hobby where your job is to gain a knowledge and hands-on learning about how your biofilter works and what it feels like to cycle it. This is the single most leveraging skill in the freshwater hobby. Additionally, towards the end of cycling you may have reason to perform some gravel-clean-water-changes and that is a skill that will eventually outstrip the cycling skill and become the most important ongoing habit. Concentrate on getting feedback from all the good hobbyist members here about all these basic things during the long weeks of the fishless cycle. Believe me, the knowledge gained will be far more important than just the thing of getting the tank cycled.
The third very important skill will be that of filter maintenance. We like to recommend that beginners start by thinking of this as a monthly thing although it can be adjusted once one fully understands the tradeoffs. Once your fishless cycle has produced a fully cycled biofilter you will be seeing zero ppm ammonia and zero ppm nitrite(NO2) in test results and it will be nitrate(NO3) that can give you a hint about how your filter maintanence schedule is going. It's nice to have a some sort of base line of nitrate that is 15 or 20ppm above whatever your tapwater nitrate is (or better of course) and to get a feel for this. Then, if your test results indicate that nitrate is creeping up on you, it will be a sure sign that a filter clean is needed. Of course, another common trigger for filter cleaning is reduced water flow. That also is a sure sign. If your habits are good and regular, you may just get nice monthly (or 5 or 6 week if you have a large external cannster perhaps) cleans and hopefully never see these signs of needed filter cleaning.
The mantra for parents of very young children like yours should be that it is always much worse trying to explain why a new pet just died. You don't want that, instead it is better to be prepared to hold the line for your fishless cycle. Get some really big poster paper and have some fun family sessions drawing scary looking cartoon bacteria! Draw big pictures of The Nitrogen Cycle and explain about how all the little passageways in the sponge are being coated with an oohey-gooey biofilm that the cartoon bacteria are growing in. Explain how there have to be millions and millions of them and share the experience of doing the ammonia tests and seeing if the millions of bacteria are eating.
For you, as an aquarist, the pristine sparkling water your good biofilter will eventually produce will feel so worth the wait. Do a good "qualifying week" to make sure those A-Bac and N-Bac colonies are large and robust and will have plenty of "drop-down" room once you do the final water change and introduce the first bioload of fish!
Good luck!
~~waterdrop~~
