Translation:The child is looking for one fluffy bunny.
Im curious as to why the numbers are being conjugated into the partitive now, and not for all the previous sections.
A transitive verb takes a direct object that can either be total object or partial object. These are expressed by the accusative resp. partitive case. Let's take an example.
Syön kakun : I eat a/the whole cake
Syön kakkua : I eat some part of a/the cake
Etsiä is also a transitive verb, i.e. takes a direct object, the object is the one you are looking for. But this time the verb has a different aspect: either you find something or not. Compare this to eating: you can have something partially eaten. (For further info about aspects see for instance in Wikipedia.) Let's change the tense to illustrate this.
Lapsi etsii yhtä pörröistä pupua : The child is looking for one fluffy bunny.
Lapsi etsi (yhden) pörröisen pupun : The child looked for and found a/the/(one) fluffy bunny.