As of 2015, you can make an "Animal Jam" account and play for free as a non-member. Non-members are able to play games and make friends, and have access to selected pets, dens, animals and adventures. Non-member accounts are also advertisement-free and moderated at all times.
To make a free "Animal Jam" account, choose that option from the game's homepage. Choose your animal, name it and then enter account information such as your birthday, username and an adult's email address. The game also offers three different membership level tiers. The optional membership includes more animals, dens and adventures, as well as additional in-game currency bundles.