Check blood sugar and insulin
In the middle of play, a film, something important: blood sugar doesn't care about timing. Having to break off for a check you didn't choose is frustrating, and a clear order makes the interruption shorter. The steps are below.

Insulin pen and meter
An insulin pen, a drop and a meter showing 120.

Meter and insulin pen
A blood sugar meter showing 120, a drop and an insulin pen.
About this visual support
The body sets the pace here, not the child. Blood sugar has to be checked when it has to be checked, whether that's mid-play, mid-favourite-scene, or just when something has finally got fun. That sense of being forced to break off something you chose for something external and imposed is one of the hardest parts, far more than the measurement itself.
Visual support helps by making the interruption small, clear and time-bound. When the child sees that the check is only a few pictures and that there's a card for back to what we were doing afterwards, the pause becomes easier to accept. The break is framed as a short detour, not an end to the fun.
A concrete tip is to let the child decide the small detail that can be chosen, such as which finger to use or where you sit. A scrap of personal control in an otherwise imposed situation makes a real difference to the resistance.
So the checks blend into the day without being forgotten, you can add them as recurring items in the Routined app, making them a natural part of the rhythm.