Bateaux:
* Ba: Like the "ba" in "bat"
* teaux: Like the "toe" in "toe" but with a slightly more open sound
Mouches:
* Mou: Like the "moo" in "moon"
* ches: Like the "chess" in "chess"
Putting it together:
* The "x" at the end of "Bateaux" is silent.
* The emphasis is on the first syllable of "Bateaux" and the second syllable of "Mouches".
Therefore, the pronunciation is roughly:
* ba-toe-moo-chess
It's a bit of a tongue twister, but practice makes perfect!