Is there an English to Coptic translator online?

I know it's late, BUT I did find something else useful in case someone else is searching for this information. It's a bit of a process and only works for single words, though.

1. Go to coptic-dictionary.org and type in the word you need in the Quick Search bar. If the word is common enough, the site will give you different ways it is translated into Coptic. However, it is in the Coptic alphabet, which leads me to:

2. Wikipedia has a handy table translating the Coptic alphabet to English pronunciation. Write down the pronunciation of each letter and string it together.

Good luck!

As Locoluis explained in his excellent answer, machine translation in general is unreliable. For dead languages, the best attempts are laughable: Google Translate's English-to-Latin, for instance, tends to produce incomprehensible gibberish.

If you really want your students to pronounce something in Ancient Egyptian, the Book of the Dead is the obvious choice. But this is not a trivial task, especially for English speakers.

The first chapter, transliterated, begins:

hrw n qrs wsı͗r ꜥq m-xt prt ı͗n [NAME]
kꜣ ı͗mnt ı͗n đħwty nswt nħħ
ı͗nk nčr r-gs dpt
ꜥħꜣ.n.ı͗ ħr.k
ı͗nk wꜥ m nw n nčrw
đꜣđꜣt smꜣꜥ xrw wsı͗r r xftyw
hrw wđꜥ mdw
n-wı͗ wnđwt.k wsı͗r
ı͗nk wꜥ m nw n nčrw

(Source.)

Notably, no vowels are included. And many of the reconstructed consonants are not easy for English speakers:

• ꜣ is a glottal stop as in "uh-oh"
• ꜥ is the Arabic 'ayin, a pharyngeal consonant
• ħ is the voiceless pharyngeal fricative, Arabic's emphatic h
• x is a velar fricative like the German "ch"
• q is a uvular stop like in "Iraq" (Arabic pronunciation)

(Source.)

The best option is probably the "Egyptological pronunciation", which is entirely disconnected from reconstructions of how the language was actually spoken, but is easy for English speakers. This is the system that gives us pronounceable names like "Tutankhamun". Transliterated, his name would be twt-ꜥnx-ı͗mn; in reconstructed pronunciation, that would be something like [taˈwaːt ˈʕaːnxu ʔaˈmaːn]. The most difficult consonants are replaced with vowels, and other vowels are inserted arbitrarily.

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.