Fun and exercise all rolled into one. The Mookie Junior Swingball is available for £5 at HabDirect. Postage is £5.95, but even at £10.95 delivered this is still the cheapest we were able to find. Stubblerash at our sister site, HUKD, found it on Amazon for £14.93, but most sites seem to sell this set for £25.
HabDirect is a 20 year old company that sells band-name equipment for fitness testing, measuring, monitoring, and sports performance, as well as fitness equipment for home use and commercial use.
The Mookie Junior Swingball is great for younger players as it is height adjustable. It has a big, 9cm soft foam ball that's easier for little ones to hit. The clip-on tails stream behind the ball, making it whizz around like a comet every time it is hit - a bit more exciting than traditional swingballs.
The Mookie Junior Swingball is suitable for ages 4 plus (it is not suitable for children under 3 years due to small parts).
One the website it says that the Junior Swing Ball kit includes full instructions for adult assembly.
Thanks to stubblerash at HUKD!