Micro scooters are great but they fall down when your child gets to the age they want to go off by themselves. I watched a four year old rocket off into traffic only last week. Luckily the relevant driver saw it before it happened.
I've been commuting for 2.5 years into central London with my daughter on her scooter. We don't get in people's way on the train, on the platform or in the street anything like we would with any other form of transport and there has never been any safety incident. How is this? A piece of string.
The leads Micro will sell you are far too long. My piece of string allows me to steer, brake and (when she is tired) pull my daughter. As my work involves me having string on me most of the time, I have attached bits to other parents' scooters to great effect. One suggested rather over-excitably that I should get a craft show (!)
So, take a piece of string about 2.25 x the length of the drop from the middle of the handlebars to the top of the wheels. Tie it to the middle of the handlebar (go over twice to make a cross then tie two half hitches (they tighten when you pull)). Tie the other end to the same place. Then start at the handlebar end and make an overhand knot (round and through) every four inches or so, leaving the last loop the length of the width of three fingers. A loop is important, as you loop it over finger and your hand can then relax when the string is not under tension without dropping it. Tying several knots means a) the thing remains neat and doesn't get tangled and b) if you have to secure the scooter to anything (bike seat, lamp-post, your shoulder, interior of a train) you can loop the string round the object and pop whichever knot is appropriate to the size of the object and the immobility you wish to achieve) over one handlebar to do so.
Now you have a scooter you can pull, brake, steer, carry and secure which unlike the Micro ones, is unobtrusive, doesn't get in the wheels, won't be stolen and costs nowt. It gives the child freedom while allowing you to take over at any time. Moreover it is short enough that you can tow an empty scooter because you can pull it up (to keep it upright) as well as along. The Micro leads just tip the things over forwards. This also means your child can go over small obstacles safely (we live by a level crossing) with just a judicious parental upward tug.
I use a flat, cotton tape about 2cm wide. It's strong and comfy (esp if you carry the thing). You may be surprised how useful you find this!