Kitten had pee accident, is this normal?

My kittens are about 14 weeks old roughly. They were both fixed two weeks ago. Theyve never had any accidents in the house since i got them, and ive had them since june 21. Yesterday my girl was napping in a hamper of clothes on my bed and i found that she had also peed on my bed once. Is it possible it was truly just an accident bc shes still little? We have multiple boxes they are just in their room, not mine. Its clean, her wound looks good, there hasnt been another accident etc

Yes, probably just an accident.

BUT, will need some pics of your avatar kitten to be sure.

Just keep a watchful eye in case of a UTI.  Hopefully it's a one-off.

Remember to clean the area really well with an enzyme cleaner specifically for the purpose.