The amount of Lego flushed down the toilet could build a 550,000 block tower 100m high, according to a Direct Line survey.
The under-10s have also dispatched four million dolls to a watery grave, along with four million pens.
The insurer’s research focuses on the cost of such pranks, since as well as 4.2 million mobile phones being flushed away, children scribble on walls, feed banknotes to the dog, and jam toys into DVD players.
One in ten (12 per cent) parents with a child aged under 10 have had their mobile phone dropped down the toilet at least once, while one in twenty have had their car keys flushed down the loo and 10 per cent have seen cash disappear round the U-bend.
But there is a serious side (if losing your phone wasn’t serious enough) - items flushed down the toilet can cause major blockages resulting in overflowing water and even burst pipes, with a plumber’s bill adding to the cost
Direct Line have offered the following tips to parents with over-zealous toilet habits:
Consider purchasing lid locks for toilets in the home to prevent children dropping items into the bowl.
Install universal outlet covers for plugs in the property for the safety of children and to prevent toys such as playdough being stuffed into sockets.
Limit home access by using doorknob locks for rooms where you don’t want the contents to be damaged or played with.
Stair guards and stair gates are an important safety tool and can also help limit access to rooms in the property.
Install safety latches and locks to keep cupboards shut and inaccessible.
Use endurance paint where you can wash away any stains, such as scribbles or colouring on the walls, without damaging the paint finish.