The mother elephant washes her baby's body in the river.
Literal
Mother [possessive-の] elephant [topic-は] river [possessive-の] inside [at-で] baby-elephant [possessive-の] body [object-を] wash-[benefactive-てやります]
小象 = baby elephant (小 small + 象 elephant). あらってやります = 'washes for (her baby)' — ~てやる marks the action as done for someone in one's care, here in polite form (~てやります). The river scene makes this vivid.