Scott bikes are pretty decent in my opinion. That one is their entry version, but it is generally a good bike for up to an intermediate rider. I believe they are only 29. That gives you an extra ‘shock’ in the sense they roll over obstacles more easily. They may not be quite as manoeuvrable in some people’s view.

The Judy is an ok spec. I am assuming it’s the adjustable air spring version. The Judy silver line is what I would describe as low-mid tier. Not a bad fork. They come in 100 and 120mm range. Since you don’t know what kind of trails you’ll encounter it’s hard to say if there’s any advantage to the higher range for you. Of course, whether it’s been properly serviced and it’s condition is something you’ll need to decide for yourself. But if it’s ok it will likely do what you need.

The X-Fusion is a bit more of a gamble. I’ve had 2 X-Fusion dropper posts and I thought they were fine. But a lot of people I heard of had nothing but trouble from them. They make an entry level product that may work out ok. It seems people are pretty evenly divided on the shock you mention. If the price of the bike works for you and you like it otherwise I’d be inclined to take the chance. You can always replace the can (shock) for a lot less than a fork.

Price depends on where you are but that seems in the range. Compare it to what you see on Pink Bike.

Let us know if that’s what you go for. Pretty exciting to be able to get out mountain biking with your boy!