Froggy and I have been studying Hebrew together for awhile now and I have found that it works best when presented repeatedly in multiple formats but also if it is relevant to her everyday life. We do "vocabulary words" that go with her letter of the week but these do not stay with her past the week for the most part.
What does work is when we use those words regularly. She knows her colors and most body parts and family because we use those words. So now we have started with the days of week, the months of the year and a few weather terms. The way we do this is very "preschool" style with circle time and lots of singing and a big wall calendar and weather station. And Froggy is having a blast. And we are both learning.