More often than not, this is how practicing violin and cello looks with my children (ages 3, 5, and 6):
1. Tell children that practicing is starting in 5 mins. Listen to moans and complains and negotiations about who is not going first and how unfair life is.
2. 10 minutes later, head to practice space. Call most compliant child. Check social media on phone.
3. After 2-3 minutes of mindless scrolling on social media, call most compliant child AGAIN, because said child isn't complying. Issue threat if they don't come by the time countdown from 10 is reached.
4. Unpack instrument for child while waiting for them to show up.