I really try stick to them doing it only while it is fun. I think the key for younger kids in particular is to find ways to encourage an independent love for it. So we often have short practices, but we really do aim for daily (lovely Suzuki saying "only practice on the days that you eat")
Sometimes we do longer practices when we are all feeling relaxed and seriously working on a particular item or technique. Other days it's a review day where we just play what calls out to us to be played.
For Dylan (3) and Nathan (5) I build a lot of games around practice - we throw balls into buckets and find what to play next, we snap snap circuit bits onto the board for each exercise done, we build duplo towers piece by piece for something practiced. Dylan practices for about 4 - 8 minutes. Nathan for about 5 - 15 minutes depending on the game, the focal point of the practice session and his mood.
Aiden likes the games sometimes, but he most often prefers to use something like this:
Warm up (scale/arpeggio and old favourite piece)
Review piece 1 (usually an old piece that may need a bit of fine detail work or has gotten a bit rusty)
New piece (the piece he is currently working on - he does the bits his teacher suggested he focus on, working on tricky bits over and over and then trying to play it through a few
Sight Reading Practice
Review piece 2 (another piece that he knows well but may need a very slight adjustment, or taking a favourite piece and playing it in a different key for fun)
Review piece 3 (an old favourite that he knows well)
That's for violin. It takes him about 20 - 30 minutes a day when he does it like this. If he only does the review pieces then it's less than 10 minutes. Then I try encourage another session later that day again.
