Minami-Senju is not a popular area of town for tourists. It is right in the middle of Tokyo's 'Shita-machi', older neighborhoods of the working class. This area of Minami-Senju, however, is brand new and so is Shioiri Park. 
Shioiri Park has all the basics: baseball fields, tennis courts, large grassy lawns, picnic & BBQ areas, and an excellent playground. Located along the Sumida River, there is also a lovely cycling course. I was also impressed that although the riversides are concrete, they left a nice section of reeds right at the waters' edge.
I was surprised by, a huge, beautiful, traditional-style building that sits between the park and the Tokyo Metropolitan College of Industrial Technology. It is actually the 'Shirahige Nishi Pump Place', a water treatment facility. What a way to hide an unsightly necessity! (It is the large building on the left below).
Minami-Senju hosts a very large train freight depot. The Shioiri Park area lies just beside it, and the entire area, including all of the residences (mostly high-rise condos), are very new. I don't know what the area was before, but its 'renewal' is very impressive.I recommend this park for those who want some wide-open space, but don't want to travel very far to find it!
The park is a short walk or bus ride from Minami-Senju Station. There is also reasonably priced parking available.
By the way, keep your eye out for English language tourist brochures of Arakawa Ward. They are excellent. I would never have know about this park if I hadn't read about it in their brochure.
The park is not very large, but there are a lot of things for children to do. First, there are some rides including a small ferris wheel, merry-go-round, mini-train, and pedal-powered 'sky' cars.
Also in the park is an 'Animal Plaza'. In addition to some caged animals (monkeys, birds,...), there is a great petting zoo. Kids get a chance to get up close and personal with goats, deer, sheep, rabbits, and really cute guinea pigs! On a second visit to the park, the petting zoo was kept clean, but the waste in some of the other cages needed to be dealt with.
Many were enjoying a couple of small fishing ponds. This area was quite popular with older elementary school boys and their fathers. 
The park also contains some grassy picnic areas, some fast food outlets, and some great blow-up 'attractions'. There was also a live music performance the day I was there (traditional Japanese drumming, flutes,...).
If you just want to look around, the entrance fee is 200 yen for adults, 100 yen for children. For 1400 yen, and adult and child can enter together and they receive 12 tickets. Each ride 'costs' one ticket for a child, two tickets for an adult. Extra tickets can be purchased if necessary.