Machine translation in general is in its infancy. Even for major languages like Mandarin Chinese and Spanish, computers have trouble with context-dependent concepts such as verb inflection and words with multiple meanings. No machine translation is reliable. All it's good for at this time is to help you get the gist of a text in another language.
Google Translate, which is pretty much state-of-the-art technology, uses a statistical model which computes the most likely translation of a word based on its context, which is generated from large corpora of text with English translations. The larger, more diverse the texts fed to the model, the better. A machine translation to Spanish will be much more reliable and accurate than one to Latin. Since there's not a lot of digitally-available Coptic literature that has already been translated to English in the first place, its highly unlikely that a Coptic translation engine will be developed in the foreseeable future.
Also, I think that you're trying to kill a fly with a cannon ball. You most certainly don't need to teach Coptic or Egyptian to your primary school students. You probably just need to give them a general overview.
Look for already-translated texts. Though for Ancient Egyptian there are texts available that deal with various subjects, for Coptic you won't find much else aside from liturgical texts, and there are a couple of interlinear Gospels around whose sources aren't quite trustworthy...
In fact, my advice for you is to stick to Egyptian Hieroglyphs. They look good, they're easier to read (!) and you can give a good overview of Egyptian writing without getting into nasty details. OTOH, Hieratic and Demotic are extremely cursive and difficult to read, and Coptic literature is mostly gospels and psalters written in an embellished Greek font (though I haven't looked hard).
This is an aside, an a personal pet-peeve of mine. There are ways in which you can write your name in (uniliteral) Egyptian Hieroglyphs or Coptic. The wrong way is to transliterate all letters from A to Z one-by-one. The right way is to follow the phonology of both languages and transcribe their sounds into writing. For Ancient Egyptian, you can only write consonants; as a work-around, write e and ee as the Quill glyph /j/, write o and oo as the Quail Chick glyph /w/, and use the Vulture glyph /ꜣ/ at the beginning/end of words that start/end with a vowel.