Big enough to ride on their own but a tad slow and wobbly to trust them on busy streets.
Or they mispent their youth on scooters and just can’t get the hang of pedal cycles.
Here are two products that should make life easier to many parents:
The Follow Me from Switzerland

It enables the secure attachment of most children bicycles (12″-20″) with these key advantages compared to tag-alongs:
The Like a Bike Junior
A more appropriate name would be Maxi. Strong enough, even an adult can ride it.

And it gives us an opportunity to quote from Mike Burrows’ Bicycle Design:
It was Baron Karl von Drais who took that most remarkable first step in the evolution of the bicycle, when he discovered that a vehicle with a pair of in-line wheels does not necessarily do the obvious and fall over… All the subsequent innovations (such as cranks, chains, etc.) were all logical and inevitable steps. What von Drais did, on the other hand, went way beyond logic or evolution. There was no precedent in nature, no natural forerunner to be improved upon. His running machine was as original as it is possible to be.
Both are in stock
5 tips for cycling with kids…
Doc Homebrew’s kids have been cycling since they were old enough to hold themselves upright in a kiddie seat, so that’s a family that knows a thing or two about riding with kids………
Andrea,
How much is the “Follow Me” and will it work with a Puky Cycke 20-3?
Thanks
Dave
The Follow Me is £145 and it will work with all Puky bikes.
[...] First we have ordered a FollowMe from Velorution (I ordered myself a Hebie chainguard to try on my fixie), that should allow us to ride to Stanwick Lakes for him to practice riding alone. The FollowMe will come with a special adaptor whatsit that will allow me to attach it to my fixie (normally it comes ready for quick release wheels). [...]