Take your own  child carseat as no-one has them.  Also, be careful, many older taxis don't have seat belts in the back or just have lap belts despite it being law to have one so there could be a problem fitting the seats in safely.  Most restaurants are friendly towards children, but few have any facilities or menus for them and none have seperate smoking areas. 

Also, Moroccans are extremely fond of small children and many people will kiss your children, or want to give them sweets or small gifts- you need to respect the culture, explain to your children before you arrive that strangers will be more friendly than perhaps they are used to and it is nothing to be scared of. Carry some wet wipes if you are concerned about hygeine.  Marrakech is a great, safe, friendly place for families with children.