The following are my thoughts on a logical progression. There are no hard and fast rules here and you may find you would want to combine some steps, reorder or jump over them. You could ignore them altogether since I don't know the people involved. Having said that .....
* I'd avoid the soldering iron for step 1. Go for the spring type of 100 in 1 kit. Reason: You want the enthusiast to have success very early and if they don't have adequate soldering skills, they may add thermal destruction to the list of things that can go wrong.
* This:
I would go for an analogue based all in one kit with a variety of experiments rather than something with a digital bias like Arduino or Raspberry Pi.
Reason: Even if they quickly tire of the analogue circuitry and component level assembly and find Arduino projects (for example) more interesting, having some hands-on experience at the fundamental level will serve them well.
* I would highly recommend good instructions for a beginner - but that can depend on the person. Some may need everything spelled out and others may just need a diagram.
* It would be good if there was someone with experience that could be available if they got stuck on something. This person could also observe the interest taken and suggest directions of exploration.
* Be prepared for every range of interest. Without knowing the 11 year old, I can only speculate. They may get bored by the end of day 1 or they may want to build their own microprocessor.
* If interest grows, I'd be adding a breadboard or two. Include some jumper wires and a grab bag of through hole resistors, capacitors and some jellybean transistors. A fistful of LEDs wouldn't go astray either. There may be other components their direction of interest might suggest, too.
* If we get to this level then we can introduce static sensitive devices and ICs
* If possible, I'd hold back on the Arduino stuff until now - but if interest jumps in that direction early, then it will be silly to hold back.
* Up until this point, connections can pretty much be solderless - but if a soldering iron hasn't been procured by now, then it's time to get one. Same with basic tools like side cutters, pliers an screwdrivers. Throw in some matrix board/proto board/Veroboard for good measure. Get the enthusiast to start off soldering with some simple circuits. It would be far better to do 20 solder joints and find you've killed 2 components than do 200 joints, killing 20. Use circuits with components that will tolerate some stress and won't break the bank if they get fried.
* By this stage, specific areas of interest are quite likely to have been established, as would the range of skills, so where you go from this point should, hopefully, be self evident.
One last point. Depending on the individual, the above "sequence of events" as it were might take a year or more - or it might take a week or two. Some areas might be engrossing or completely uninteresting. They may fly through some concepts or they may take their time. This is something for which you will need to prepare yourself. It could be rather unpredictable.
Just my 2 cents' worth.