Monstrous Mammoths

Meet the Mudcrusts! Lowbrow Mudcrust is the lumbering, lazy head of the
family, who is happiest when he is squelching his toes in the slime.
That doesn't stop his wife Flora from nagging him and reminding him
that he's not the chief of the tribe. Their two children, Bogweed and
Fungus, are always fighting. Although Fungus doesn't have Bogweed's
brute strength, he is does have more brains.

The third book in the Mudcrusts series, in Monstrous Mammoths we
discover that the problems of the Mudcrusts are not over yet. They've
escaped the destruction of their hut and battled against sabre-toothed
tigers, but there's more trouble in store.