Collectible items are a good form of investment as they grow in value with time. The craze for sports and other entertainment memorabilia is especially strong in the US.

Recently, Goldin Auctions, which specializes sports memorabilia auctions, listed a complete set of first-edition Pokemon cards from 1999 on its website. It was sold at $107,010 at the auction. The set was in mint condition and included a rare holographic Charizard card, a CNBC report said.

What fetched the set such a high price was the fact that it was graded at "GEM-MT 10" or "Gem Mint" by authentication body Professional Sports Authenticator (PSA) which assesses the cards' corners, color consistency and gloss. The "Gem Mint" grading means that the cards were in "virtually perfect" condition.

The bidding for the set started at $25,000 and received 12 bids.

The auction house has been seeing a sudden rise in value of Pokemon cards that are becoming as important as sports cards.

"For many Millennials, the original 1999 Pokemon video (and) card games remain a staple of their childhood, providing what seems like a lost art in a nostalgic feeling," the listing said.

The secondhand market for what we consider as a child's toy is bigger than you thought. A 2018 research by Russia's Higher School of Economics revealed that some sets of Legos (a line of plastic construction toys that are manufactured by The Lego Group) has an extremely high value when sold second-hand. It is said to fetch higher returns than gold, bonds, and stocks. Their study of 2,000 Lego sets revealed that while many yielded a return rate of 11 percent, some were sold for a whopping 613 percent.