It's a terrace with artificial grass located on the northeast side of AEON MALL Ibaraki (towards JR Ibaraki Station), next to the Welcome Entrance.
AEON MALL Ibaraki Facility Guide｜AEON MALL Ibaraki
Surrounded by planters and equipped with various shaped chairs, it seems like a comfortable space for families with children to relax and enjoy.
The JR Kyoto Line runs right next to it, so it might be a fun place for children who love trains!