Tomi Ungerer's series of illustrated books for children featuring the Mellops, an anthropomorphic family of pigs, is over fifty years old, and it shows.

The story, of a treasure hunt following the discovery of an ancestor's letters in an ancient chest, is familiar and resembles Red Rackham's Treasure, Tintin's classic adventure set on the high seas that was one of the source books for the recent Spielberg film.

The Mellops get stuck on a desert island, "when they realise that riches are no good to people stranded where there is nothing to buy", and have to build a fire to send up smoke signals as an SOS to a passing ship.

Plenty happens in the book and there are numerous cliffhangers, but the story wasn't told dynamically enough to hold Isobel's attention. Instead, it was the details that grabbed her, such as the Mellor's dog in a diving suit looking at a seahorse on the cover, Isidor Mellops climbing trees to knock down coconuts, and the cream cake made by Mrs Mellops at the end. And she did find the "very dangerous" octopus scary until it was pacified by a Merpig's (the porcine version of a mermaid) music.

Of the Mellops themselves she had little to say, suggesting that Mr Mellors and his four sons were not sufficiently individualised, and she thought the monochromatic illustrations in this beautifully produced book could do with more colour, specifically pinks and reds.

I found the language slightly dated, not as snappy and breezy as in contemporary picture books. Overall, a picture book classic whose time has maybe passed, though Isobel did express interest in reading more of the series.

If you would like to become a family reviewer, email us at childrens.books@theguardian.com