If you use the bed for your 2 year old....just ask the cabin steward for a mattress pad, and you will have no problems with any split in the bed. There is no way anyone could fall between the split of the bed.
I seriously doubt any dangerous situations have been reported where a passenger has fallen between the split of the beds.
That's not the cause of infant/toddler deaths when sleeping in an adult bed. Consider the following, which you can find if you google the topic:
"The main causes for suffocation in adult beds were getting wedged between the bed and the wall, stifled by soft bedding, or overlying, which is when an adult lies on top of the baby, the study reports.
"Babies lack the motor skills to deal with environmental risks. They can't roll over or push things off their face," Kemp says."
"Babies can suffocate when...
•Sleeping with adults or other children
who may roll over on baby
•Slipping off the chest of a sleeping adult
and getting trapped between the adult
and bedding or sofa cushions
•Sleeping on a soft surface like a pillow,
pillow top mattress,memory foam,
sheep skin or comforter."
I make the same recommendations as Lisa, a crib or sleeping bag, depending on the age and ability of the child.