We will not ban a player if they use alternate accounts to play Adopt Me as long as they're using that account for reasonable purposes, such as ageing up pets, using them for lures or claiming the advent calendar. 

We do not condone using alternate accounts to hide from your main account and perform activities that break our community guidelines, such as cross-trading, gambling, hacking, scamming and evading a ban. Any main and connected alternate accounts will have their access removed from the game if found breaching regulations. 

Is there a limit to the number of alternate accounts I can have?

If you're not using the alternate account for malicious purposes, such as the ones addressed above, you can use as many as you like if the accounts align with Roblox ToS.