If it's Applejacks, which is Warrington, it shut at the beginning of the month. Like wessexgirl says, it's harvesting time.
My dcs are 4.8, 3.1 and 21mo and we haven't taken them yet, despite being surrounded by them where we live. I don't think they're old enough to find it exciting and they certainly wouldn't be able to help us find our way round. Plus, I'm a bit worried one would disappear .
We've been twice to our local with DS 2.11 - he loved it, just tore around the paths and occasionally through the corn. I had no choice but to follow. We didn't begin to find our way to the middle, but our one there were lots of stamps to collect on the way which were reward in themselves.
Ours is open through September, but we are further south which may make a difference.
The proper Maize Maze is closed, they do other events but the website says they are suitable for over 3's. There's a Haunted House, a Haunted Hayride and some other bits but I doubt your 21mo would get much out of it, tbh.