Dedicated cycling families can be seen of a weekend out for a run on specially built or adapted tandems and triplets1. But with tandems running into hundreds of pounds and triplets costing well over a thousand, this is a rather expensive (if agreeable) way to travel en famille.
If your children are small, you can have most of the fun of a tandem by getting a trailer bike (sometimes known by the brand name Tag-Along). This is the back half of a bike with a long pole which attaches to an adult cycle - the host bike - making an articulated three-wheeled, two-seater contraption.
The best thing about a trailer bike is that it's a cheap way to take small children cycling. Experience shows that it's a popular activity and gives them some fresh air and exercise. Compared to riding with small children on their own bikes, you can also move faster and further, making a proper outing possible - say along your local river towpath to a nice tea shop, or maybe through some woods. It's also safer, giving you complete control over where your child cycles - behind you.
It is surprisingly easy to tow the trailer bike, even if the small person is not up to pedalling all the time. And you can get the occasional surprise push from behind when you need it (or when you don't!).
And there is a ready market for second-hand models, so you should be able to get back around half what you paid when you've finished with it (as long as it's in good condition).
Not So Good Points
A bike with a trailer bike behind is long and somewhat unwieldy. Although it rides fine (you won't notice except in the tightest of corners) it can be hard to get through the gates which are put on many cycle paths to stop motorbikes and cars from getting in. If you hire a trailer bike to ride along a national cycle route, the hire shop may have keys for the gates, which makes life easier.
The small person is also at the back and low down, so use of a flag is essential (this is normally supplied). This position also means that unless you have full mudguards on the host bike, little Johnny is likely to get quite muddy (note for parents: best not to use the best school coat in this scenario). For safety it's nice to have another adult riding along next to the tiny (they can also have a nice chat about all the interesting things one can see while out cycling).
The trailer bike can make the host wobble a bit, so you need a good stiff host bike (most mountain bikes are fine). Large, heavy children are better off on a proper tandem.
There are several questions which spring to mind; here are some answers.
Is it safe going downhill? - Yes, as long as you keep the speed down. Bike brakes are not terribly effective at high speeds, and can fade alarmingly, so make sure that you keep the brakes covered and check that they are still capable of stopping you.
Doesn't the back tend to slide sideways? - Not in normal use (including muddy tracks). The weight of a child low down over the back wheel keeps everything in place.
Can my bike brakes cope? - V-brakes cope easily with the extra load, classic cantilever brakes might be nearer their limits. Tow with a mountain bike equipped with V-brakes and all will be well.
Can you get them with brakes attached? - The common ones don't have brakes even as an option, but there's nothing stopping you from fitting them if you feel so inclined. You might want to cable the lever back to the host bike in some way and run it like a tandem drag brake.
How much fun is it? - More than we are legally allowed to describe on a site fit for family browsing.
Choosing and Buying
There are several features to look out for on trailer bikes:
Folding - Some fold along the towbar, others such as the Adams Trail-A-Bike just in front of the seat tube (which makes the folded package somewhat smaller). Folding is a must if you want to get the trailer in and out of a car easily.
Alloy wheels - Always buy one with an alloy wheel if you can, they are stiffer and lighter, and don't rust.
Spare brackets - A spare bracket for each potential host bike is easier than moving one bracket around.
Attachment point - The best ones attach on a special carrier rack (a good example is the Islabike from Isla Rowntree), but these are very hard to get hold of and mostly second-hand - not necessarily an issue, but finding them is.
Gears - These are good for older kids, but for children under five they make no odds.
Suspension seat-posts - Many trailer bikes now have these, and they are a good idea because the little ones don't see the bumps coming.
Mudguards - Fit them to the trailer and to the host bike!
Buying second-hand is easy, there are plenty around; check your free ad papers and the classified sections of cycling magazines. Make sure all the original bits are there (especially the flag and the shims for the host bike seat post) and the instructions.
Follow the instructions carefully. Don't ride over the recommended maximum speed (usually about 16mph, quite enough for most leisure rides) and don't use them after dark unless you have to and have lights absolutely everywhere, specially on the back of the little tyke's helmet.
Always use a helmet! Children in particular need the protection. Cycling is safe, but so is driving and look how many people die in car crashes every year.
That about wraps it up for trailer bikes, a great way to spend quality time with the children.