How d whale iz a mammal?

The current topic in school is that of animals, insects and birds. The brat was sitting glazed eyed through a long drawn out explanation of mammals by his tuition teacher. Mamma cringed as she overheard bits and pieces of the discourse floating into the bedroom where she tried to arrange the chaos in brat's cupboard into levels that didnot guarantee immediate annihilation by alien life forms growing beneath the piles of disarrayed clothes.
The teacher: Brat, listen carefully, what is a mammal?
Brat, with surly disinterested tone: Wot iz a mamul?
The Teacher in tones so droning, they could be patented for a cure for insomnia: A mammal is warm blooded, has fur on its body, gives birth to its young and feeds its young milk.
Brat: (Repeats the litany, without any seeming registration or interest): Iz wom bluded, wid fur on d body, gives burth tu its babies and feeds dem milk.
Mamma scrambled in his bookshelf for his encyclopedia on animals to hand over to the teacher to spice up thing, when she hears an alert brat voice pipe up.
"But den, how d whale iz a mammal? Is nod got fur and how id can feed his babies milk in d water?"
Any answers? This is what Mamma googled up, and plans to answer the brat with today. Though, unless he physically checks out the hair on a whale, and sees any baby whales drinking milk from their mammas, I doubt he would be very convinced...he's not a trusting soul, this child.