This child is severely dehydrated. 

This child needs 20 cc per kilogram of normal saline IV now.

The child may need another fluid bolus subsequently.

Colletti JE et al. The management of children with gastroenteritis and dehydration in the emergency department.  The Journal of Emergency Medicine 2010; 38(5) 686-698.

Evidence on the assessment of dehydration, methods of rehydration, and the utility of antiemetics in the child presenting with acute gastroenteritis

Moritz ML & Ayus JC.  Intravenous fluid management for the acutely ill child.  Current Opinion in Pediatrics 2011; 23, 186-193.

Oral rehydration therapy and early refeeding in the management of childhood gastroenteritis

Link: CPS Website