"All mice are small."
Translation:Alle muizen zijn klein.
"Elk" is best translated as "each". It refers to every individual within a group. I think it is mostly synonymous to "ieder" (every)? Somebody correct me if I'm wrong. Some examples:
"Alle kinderen krijgen een snoepje" - "All children get a candy"
This could theoretically mean that they have to share one piece of candy! That would be terrible.
"Elk kind krijgt een snoepje" - "Each child gets a candy"
This makes it completely clear that every individual child gets his/her own candy.