Sepron the Sea Serpent is the second book in Adam Blade's Beast Quest series, and it's much the same as the first in terms of quality. It's not a bad book by any means, but it's particularly fascinating either.
In Sepron the Sea Serpent, Tom and Elenna have just recently freed Ferno the Fire Dragon from Malvel's spell, and next on their list is the titular sea monster. Like Ferno, he has been magically enslaved by the nefarious wizard, and they'll need to unlock the chain around his neck to free him.
Obvious to the point that it needs no spoiler tags, they do so successfully... and without much hassle, really. I suppose it's to be expected that there won't be a long, exciting battle sequence in a book that's only seventy-six pages, but I admit that I found it quick and unexciting. I'm hoping that over the next few books in the series, the plot gets a least a bit more entertaining; as of right now, I can hardly see anyone older than the target audience (RL3) finding the book particularly entertaining.
As said in my Ferno review, this could be a good first fantasy series for young children. As the books are less than one hundred pages each, they're best suited to children beginning to read chapter books or parents reading to their preschoolers.