For non-Arabic speakers, building up Arabic vocabulary with our children is something which may feel unnatural to begin with as new words and phrases are introduced. But with practice and use, they will soon roll off our tongues without any thought inshaAllah.
It simply takes time, practice, patience and the belief that growing our language skills will one day pay off and will become second nature bi'ithnillah.
People learn second languages all the time. The difficulty we have in the West when learning Arabic, is we are not often in situations where we are forced to speak it, so we don't. We're learning to understand and speak Arabic in a non-Arabic speaking country so its too easy to stay within our comfort zones and not try...even when we meet an Arabic speaking sister at the masjid.