How I make it happen, first I make sure I have at least 2 tables with high chairs at them (assuming you have one toddler). When I get my sim to the restaurant, I first have the child come to the location. Then after that I look to see which table is free and click on the table to request that table. Then before ordering I have someone put the toddler in the high chair. Usually the toddler is pretty hungry, and I before ordering, I click on the high chair to have the parent give them some food. You can cancel the interaction for the toddler to eat that food until you are ready for them to eat. Finally after that, I have some one order the meal.