Radio Control modelling is a great hobby that can encompass cars, boats, planes and helicopters.
Cars are the usual starting point with most children starting out with ready to run 'toy rc' type cars, the ones that come ready made and that run on 'AA' batteries.
These are great but they grow out of them or use them to destruction and then it's time to buy another one. The answer to this is to buy a model that you can get spare parts for or even better, upgrade parts that can make it look different or go faster.
Once you have some experience of how 'proper' radio control models work, you can expand your horizon to a simple aircraft or helicopter or if you are fortunate enough to have a suitable nearby lake you could even get a yacht or a power boat.
With the right model and electronics this could serve as a starting point for building your own models, radio control systems can be used for many different things and are a great learning tool for people interested in engineering and how things work.
A hobby for all ages. There are sizes to suit all budgets and spaces, ranging from N gauge (1/148 scale) to G scale (1/22.5 scale) garden railways. 00 (1/76 scale) is the most common with well known brands such as Hornby and Bachmann. Trains sets are a great starting point if you are new to the hobby, but if you have previous experience then you can buy a wide variety of track, rolling stock and control systems to suit your budget and ability.