I'm surprised you're running low on tests already after only a few weeks! The API master test Kit is usually recommended on here, I bought my API ammonia tester for example in June, I tested every day during a long fish in cycle and then weekly since it finished... I've still got at least 1/4 of the solutions left! The API Kit is about £20 online and lasts ages.
tbh, the general consensus is fish stores tend to either not understand the cycling process or give bad advice as they know three fish will likely die and need replacing hence more cash for them.
You will now be in a fish in cycle, there's info about that in the beginners resource bit, I'm not gonna lie, it takes a while, and it's hard work, but it's doable. To give you a rough idea, you need to be testing for at least ammonia and nitrite daily, sometimes even twice a day, and changing large amounts of water (way over half) every time either of these levels are over 0.25 ppm. If you do a water change because of a high level, wait an hour, test again, and if necessary do another change till the levels are as close to zero as possible. I lost a fair few fish before I joined this forum and realised where I was going wrong, essentially, the most important things to now are ammonia and nitrite are toxic to fish. They can poison them, and although they may not die straight away if they have been exposed to high levels of either of those they will more than likely have a shortened lifespan and be more prone to disease.
Good luck, and I really would test now and change the water as necessary according to the results. I doubt your kids would like to wake up to sick or dead fish, mine certainly didn't like it! It's also much kinder to the fish, and now you know where you can get a longer paying cheaper test Kit