``The trouble is, now that the twins can sort of walk, the house is shrinking,'' reports the eldest child, whose nursery- school rabbits are regular weekend visitors that swell the ranks of the many resident pets: her home is bursting at the seams. A search turns up several unsuitable alternate houses—they are too big or too decrepit, or have mice or odd smells. The happy solution (as in Shirley Hughes's The Big Concrete Lorry, 1990) is a homemade addition. All this is recounted in amusingly realistic detail, nicely amplified in the author's sympathetic, charmingly comical illustrations. (Picture book. 3-8)