I look around for a word ...

http://www.hiraganatimes.com/index.html

>>It might be better to simply say "Kore, oishii desu." And "Anatatachi no shokuji wa tanoshii desu." is rather "acceptable", but sounds a little bit theatrical to me. I don't know why.<<

"Kore, oishii desu." is "This is delicious."

"Anatatachi no shokuji wa tanoshii desu." sounds like "Your meal is enjoyable/delightful." This is not equal to "Enjoy your meal."

You can also simply say "Meshiagare" and to me it sounds the most natural.

"Meshiagare" is the very neutral expression.