FORD 2003 Explorer v.4 - Manual (Page 137)

Your vehicle has LATCH anchors for child seat installation at the seating
positions marked with the child seat symbol:
Never attach two LATCH child safety seats to the same anchor.
In a crash, one anchor may not be strong enough to hold two
child safety seat attachments and may break, causing serious injury or
death.
Seating and Safety Restraints
137