Santa Clara, Calif. • If you happened to be at the Jump On In bounce house in Boonton, N.J., on Wednesday, you saw quite a sight: a 6-foot-4, 266-pound NFL running back flailing about on inflatable castles and slides like a first-grader hopped up on SweeTarts.

That running back was the 49ers' Brandon Jacobs, who took 6-year-old Joseph Armento and his 4-year-old brother for an outing they likely won't forget.

Armento is the New Jersey boy who, when told the hometown New York Giants could no longer afford to keep Jacobs, emptied his piggy bank — all $3.36 — and sent it to California in an effort keep his favorite player with the Giants.

Jacobs was touched by the gesture and told Armento's mother, Julie, that he would be in the area this week while he packed and moved his family to the Bay Area. He thought his original idea for a meeting place, Chuck E. Cheese, might cause too much of scene. So they settled on the bounce houses.

Jacobs, 29, brought his 5-year-old son, Brayden, and the four kids — Jacobs included — played nonstop for nearly two hours. No one even took a water break.

"He told me he really wanted to get out there with the kids," Julie Armento said in a phone interview. "He really wanted to enjoy it, and he did. It was amazing."

Said Jacobs: "It was just us in the whole place, and we were just going room to room — just bouncing and flipping all over the place, hitting each other with balls, sweating, our shirts filthy. We were just dirty, stinky boys, you know?"

Joseph was blown away. Jacobs also gave him a signed Giants football helmet. Jacobs signed it with his former number, 27. (He wears No. 45 with the 49ers.) It reads: "To Joe: Thanks for being a fan. God bless, Brandon Jacobs."

Jacobs had one final gift for Joseph — a $5 bill. After all, Jacobs ended up signing with the 49ers, so it was only fair the boy get his piggy bank money back.

"He had some interest in there just for being a good kid," Jacobs said. "He's worth a lot more than that $5 bill I gave him."