Well, right up until the day Radar wandered into the grass, bored out of his mind, and noticed that it was considerable taller than he was. Nothing clicked, save for the vague notion that he should probably not fire his cork gun in there, since he would never be able to retrieve the cork later. He slung the gun across his back and moved on, forcing his way through the thick pasture.
"Can't believe a cow would eat all this," he muttered to himself, looking down. "Maybe I can find a snake or somethi--hey! MOUSE!"
Disregarding undergrowth, Radar hurled himself in pursuit of the mouse. The mouse led him on a merry dance through the grass, finally escaping when the boy, as was inevitable, tripped. At eleven, Radar was not exactly a model of grace.
The boy groaned and rolled over on his back...and kept rolling when he landed on his gun. "Ow," he grunted, trying to decide if the stars he saw in his vision were made up of similar constellations as the ones he'd created earlier in the day with his header out of the tree. He quickly gave up mental astronomy as a useless pursuit and sat up. "Wait, where...?"
Radar was not terrible with directions, but as he took a look around, he realized that he was decidedly lost. He dug around in carrying bag that he had belted to his waist (it was made out of his old jeans and sewed on his mom's sewing machine, much to her displeasure on both counts), but could't locate his compass. He did find the multitool that he'd swiped from his dad and took a few moments to try to make a reed whistle, but the grass wasn't hollow enough for that.
He wrinkled his nose and stood up. Nope, the grass was way too tall to see over, even jumping. The grass underneath him was surprisingly bouncy, though, so he started folding some more down into his landing zone and bouncing on it, just for fun.
A few moments later, he spotted the trail that he had come through--the grass had stayed parted, marking the place he had run through. Glancing down, he took in the nest he'd made. Then he was crashing though his tunnel back to the outside world.
Nemesis was playing with Legos in the basement when Radar crashed into the house. Literally, in this case--he'd missed his grab for the door handle and slammed into the door at full speed. (Again, not exactly a model of grace here.) Nemesis, being a bit more reserved than his older brother and used to his rambunctious ways, didn't look up until the yelling started.
"NEMESIS! QUILL! SQUIRREL! C'MERE!!"
"Radar!" Mom scolded from the kitchen. "Slow down, stop shouting and go find them! Quietly!"
Radar gave her a look of long-suffering. "I stepped in dog doo. I don't think I should do that. NEMESIS! QUILL!! SQUIRREL!"
"Then go wash your feet off and put your sandals on!" Mom ordered.
"It's summer," Radar pointed out, as befitted one to whom footgear was only to be worn during the winter, and then only when his mother caught him.
Mom sighed. "Go wash your feet off--GET OFF MY RUG!!"
"But I just mopped!" Radar protested. "I don't want to stand on the floor!"
The budding argument brought his siblings to the main floor to enjoy the scene. Radar quickly switched tracks. "Hey guys, come outside, you gotta see something!" He popped back out before his mother could catch him.
Curiosity won the day. His siblings joined him a few moments later. "What is it?" Quill demanded impatiently.
"Want to play Mice?" Radar asked.
His siblings exchanged dubious looks. "Radar, Mom said we couldn't do that anymore after we tore her blanket making the fort last time," Nemesis pointed out.
Squirrel shrugged. "Do you have snacks?"
The oldest grinned. "I found a better place to play, and no," he responded. "Come on!"
They trailed after him to the start of the prairie grass. After a quick hunt, Radar found his tunnel and led them through it to his nest. "This is my house," he announced proudly.
"How'd you find it?" Nemesis asked.
Radar grinned. "I made it. Like this." On his hands and knees, he tromped out another tunnel that ran about ten feet before folding down and stomping out the grass to make another nest. "See? What do you think?"
He was talking to thin air. The others had scattered to start tunneling out passageways and nests. Radar grinned and began adding rooms to his mansion.
That defined a great deal of the summer. By its end, the two acres of prairie had been riddled with passageways and houses--sometimes because the kids couldn't remember where their original work sites were and would restart elsewhere and build until they hit their old stomping grounds. This added an almost archaeological element to it, as they would re-explore the old paths and houses and try to figure out what belonged to who. Also, because he was the only one who insisted on running through the passageways, Radar used most of the Band-Aids in the house due to grass cuts and skinned knees.
Then Dad mowed it down in the fall...which was okay, because by that point Radar noticed that the resident mosquito population of the woods had decreased and dragged everyone out that direction at every opportunity to play Robin Hood. The Little Houses on the Prairie were never reestablished--the advent of the horses the next year kept the pasture short.
However, Mom quickly curtailed Radar's replacement game, a reenactment of medieval jousting. Something about being too dangerous...so Radar invented Bike Tag.
Apparently, he couldn't have fun without helping fund the medical industry. Go figure.