If you let 3 year old share a chair at a meal....they will spill something.
If they spill something...they will want to change clothes.
If you let them change clothes...they will come out of their room wearing shorts and a t-shirt in December.
If you let them wear the shorts and t-shirt...they will complain of being cold.
If they complain of being cold...they will convince you to snuggle in bed with them to get warm.
If you snuggle in bed with them...you will fall asleep.
If you fall asleep...the twins will climb on the cupboards and get into the cookies.
If they get into the cookies...they will spill on their clothes.
All because they shared a chair.