Parents hoping to nab the hottest toys this holiday better hit the shops early, or risk missing out on getting the top electronics, dolls and games on their kids' wish lists.

The first holiday season without Toys R Us is going to look very different for parents. While department stores, grocery chains and even drug stores are picking up the slack this holiday season, they may not have stocked enough inventory to meet demand.

"Usually, it is normal to be out of stock on the hottest toys towards [Christmas], but this year could be worse than usual," Steve Reece, CEO of toy consulting firm Kids Brand Insight, said in an email to CNBC. "Other retailers are less committed to the [toy] category."

Toys R Us had accounted for about 15 to 20 percent of all U.S. toy sales last year.

While companies like Target and Walmart have expanded their toy sections for the holidays — Target reallocated 250,000 square feet of permanent retail space across 500 locations just for toys and Walmart expanded its assortment of toys by 30 percent at all of its locations — come January, much of that space will be replaced with seasonal items like Valentine's Day gifts and candy.

The same can be said for retailers such as Kohl's, J.C. Penney and Best Buy that have also cleared more shelf space for toys.

Toys R Us' had massive 40,000-square-foot warehouses to stock toys year-round, while big box retailers sell so many different products that it's risky for them to stockpile a lot of toy inventory just for the holidays, said Richard Gottlieb, CEO of Global Toy Experts.

These stores don't want leftover products that they would have to heavily discount post-holidays, so they are more likely to have been conservative when placing orders for toys earlier in the year, he said. Toys R Us could stock toys without the fear of having to discount them in the new year.

Parents on the hunt for some of the hottest toys this year — like L.O.L. Surprise, FurReal Pets' interactive Chewbacca and the Don't Step In It board game — will have to move fast before they disappear off shelves early in December.

Target spokesman Lee Henderson said the company has been "proactive" in stocking up its toy inventory this year. He said that it's a few weeks too early to determine which toys will be the most in demand, but that Target has made sure to stock up on toys on its top toy list and of last year's favorites.