With kids that age, do not expect them to sit and listen.... for even 1/2 hour straight.
Keep things in like 10-15 minute sessions.
They cannot read.
They do not know their alphabets or numbers.
Mostly at this age, it is about socialization.... listening to direction.... circle time.... story time.... patterns, etc.
Doing 'lessons' like in simon-says or copy-cat type activities. ie: Let's clap our hands.... (as you count) etc.
Sure, 1 bible story a week. But how LONG is that story???? Kids this age, are not about 'novels.'
Board-book type books, with PICTURES in it.
As far as "memorizing'... well who knows if they can do that. BUT the verses should be SHORT. 1 sentence at the most.
They will NOT be memorizing entire psalms. For example.
AND... I would think, that there would HAVE TO BE... another Adult in the room with you.
There IS a child to Adult ratio... in school.
Because YES, what if you have to use the bathroom???? Or take them??? Then what?
YOU MUST ASK THE DIRECTOR THAT... about IF you will be having an assistant. It is imperative.
To get their focus, you can either clap your hands in a certain way, or use a bell... then in time, that will 'signal' the children... as to what is coming up or when to 'end' something. AND you verbalize this to them. So they learn that "patterning" in class and per the daily class routine.