For a twinkler, flashcards are very versatile.
I start teaching the young twinklers to recognize a twinkle rhythm. As soon as they master this we do it to break up practice sessions. There's something fun about flashcards for a 4 year old.
The twinkle flashcards are also a good way to decide what to play next during practicing. My 4 year old has learned all variations of twinkle and we have to play them all every day. However, she HATES when I tell her what to do, so she chooses a flashcard and plays that particular twinkle.
Other flashcards that I use to break up practicing or lessons are note value cards (quarter note, half note, eight note, quarter rest, etc.)
I'm also starting note flashcards with my early twinklers and they are really picking it up. I start with the open strings, then the A string notes, E string notes, etc.
I don't do flashcards everyday, but it is a great excuse for a child to put her violin down and have a little break - but still be learning.
You can download these twinkle rhythm flashcards here at The Practice Shoppe.