As a waiter in an Italian restaurant told me when I complimented him on how kid-friendly his establishment was, his smiled response with a glance at DD1 was "we were all that size once".
So for those restauranteurs who have yet to realise this - go wild - soyez raisonnable, demandez l'impossible!!
A few suggestions for starters (pun intended):
Highchairs (obviously) where you can strap the children in.
A place where you can put the pushchair without having to fold it up.
Bring Crayons and colouring-in sheets and a small bowls of crudités to the table without being asked.
Have the option of a "baby-tapas" (i.e. several small bowls of different kinds of food in case the kid turns up its nose up at one type of food).
Have a baby-changing table in the disabled loo or somewhere where you can park the pushchair easily.
Have the loo-seats which are also suitable for small children.
Ask whether the parents want bibs and beakers just in case they have been forgotten.
Have the loo on the same floor as the restaurant.
No added salt in children's dishes.
Plates and cups which won't smash if dropped.
A sideroom with a comfortable chair where Mum can breastfeed in quiet (if she wants some privacy) with a water fountain.
There must be more...