"There are at least twenty children here."
Translation:יש פה לפחות עשרים ילדים.
Usually you can only use numerals in the language you're starting from (in this case, English), not the target language, because those of us learning from scratch need to practise עשרים etc. So if you use the numerals going to Hebrew, then it will likely be marked wrong.
If you use the numerals writing in English and it gets marked wrong, then you should report it. I'm pretty sure those should be accepted.