[woodcote]

Hi Gary. Exciting plans

• Scale - 1/24, 1/32, 1/43 or HO? It all depends how much space you have and what you prefer - for yourself as well as the grandchildren.
  
• Analogue or Digital? How many of you do you want to be racing at the same time? Analogue is traditional traditional one-car-per lane racing - the controller controls the lane. Digital is multicar racing - up to six cars can race on two lanes, the controller controlling the car's speed and lane-changing. Digital is more complex and more expensive.
  
• Retro or modern gameplay? Do you want traditional slot car racing - like we did it in the 60s & 70s - or also have modern electronic gadgets and gameplay, like fuel consumption, tyre wear, pit stops etc...
  

Carrera is widely available in the US - their main product is a track system that is designed for 1/24 scale cars, but also perfect for 1/32. It comes packages as traditional one-car-per lane (analogue) 1/32 scale Carrera Evolution, multiple cars on two lanes (digital) as Carrera Digital132 and Carrera Digital124. The cars are robust. Carrera also produce a 1/43 scale Carrera Go!!! system that is aimed more at younger racers and is better suited for smaller spaces. It offers an excellent range of track, very-robust cars and accessories - including some neat electronic gadgets, some linked to app on a phone or tablet.

Scalextric have a good-value 1/32 scale range - both standard analogue and their ARC Pro digital. You fit more track into the same space than Carrera. There is also a premium analogue ARC Air system that offers many of the gameplay features of ARC Pro, but is one-car-per-lane. Although Scalextric have some beautifully detailed cars, they also have a range of robust 'Super Resistant' models ideal for beginners. Scalextric's system for younger racers is the HO Micro Scalextric. At 6 years old, your grandchildren have probably already outgrown this. All the Scalextric sets have the option to limit power (and speed) using a switch on the controller or settings in the ARC app - this is very useful for beginner racers.

Racemasters / Tomy AFX still produce the best HO sets and - in my opinion - is the only HO system worth looking at. The modern set cars are quick and have traction magnets, so are well suited to younger racers. All sets (I think) come with the Tri-power pack, which has beginner, intermediate and advanced power settings. Racemasters produce some very nice HO cars, but almost all other HO cars - past and present - will work on the AFX track.

I hope that helps!