Tablets and phones to keep children quiet at restaurants are an easy short-term solution. They also prevent the developmental skill of being bored, sitting at a table, and conversing. The 'easier meal now' trades against the slower development of social skills.
What works instead
Bring small bag of analogue activities (colouring, small books, paper). Talk with the children. Make conversation with each other so they observe. Accept that some restaurant meals will be challenging.
Within 6-12 months, children who eat at restaurants without screens become substantially better at the social skill of eating out. Children who always have screens never develop it.