Metathesis

Metathesis is the reversal of linear order of segments.

In other words, it is when children switch the order of sounds or syllables in a word when they are learning to speak. 

Examples are shown below.

'ask' /æsk/ -> 'aks' [æks]

'cup' /kʌp/ -> 'puc' [pʌk]

'animal' /ænəməl/ ->

'aminal' [æmənəl]