The disease may be contracted by ingesting contaminated material, or absorbing the virus through a break in the skin, among other things. Migratory fruit bats have been shown to be a reservoir for filoviruses, and it may be that the child either ate contaminated fruit, or played in an area where there were bat droppings (or for that matter, a dead bat).
Kids, from observation, are pretty much the same until culturally imprinted with behavioural standards, and at that age are constantly tasting things or just sticking their fingers in their mouths or rubbing their eyes. Contact with the contaminated material followed by mucous membrane contact would be all it took.