My son took part last year aged 6 and LOVED it. I say this as a parent of a child who often grumbles about activities and hates trying things out especially for the first couple of weeks. With All Stars I was shocked, he ran off straight away and joined in fine, and has been asking when it starts again this year for ages (obvs have signed him up again!).
An earlier poster mentioned parental participation; at the club we chose there were 90 children signed up to All Stars and they had loads of coaches or older teenagers helping out so no parental help or involvement was needed (although if you wanted to join in and help you could have done - most didnt as preferred watching from a deckchair with a glass of wine) HOWEVER I know another local All Stars club did have a lot more parental involvement where you needed to join in. So my advice would be ask the club you are thinking of and perhaps join a bigger club which has more support if you can.
I'm really pleased there is now a follow on to All Stars called Dynamos which caters for 8+ as I think this will work really well to keep up the sport. .
What I liked about All Stars was that firstly the price, £40 and you get 8 sessions (if it rains and gets called off they organised a catch up session) plus all the kit - a personalised t shirt, ball, bat, bag, cap, rucksack, activity booklet which my child was really excited to receive and made them feel like part of the gang when they turned up for the first session. Then also the club we chose was super welcoming and friendly, the activities they did were suited to all abilities and aimed at being fun and varied, and has given my child a real interest in cricket precisly because it was fun and welcoming.
I'd really recommend it, as im sure you can tell from my post! As well its such good value for money that even if your child didnt enjoy it its only 8 weeks and not too expensive, plus they get all the kit. And if your older one can take part too then thats really nice, plus hopefully your club has a bar and you can relax in the sunshine and watch with a drink?!
The one thing I would say is if you sign up, try to do it at least 3-4 weeks before the first session starts as it took us about 2 weeks to get the kit (they say 10 days I think) and it only just arrived before the session started, so leave plenty of time for that. I've seen other reviews online mentioning the kit taking a while so worth knowing as everyone wears it and your child might feel a bit put out if they go along to the first session and dont have all the gear with them.
If you have any other questions just ask and I will try and answer