I think it will be okay for you and your husband to have another child. Remember a new added child in your family serves as a blessing from God so cheer up Arvi.
Maybe he was stressed that's why it happened. The only advised I can tell you is that talk to him about what happened and advise him that he's now a grown up kid and must pee on the toilet.
To have a quality time with my kids so that we can relaxed and at the same time learned new experience especially for them since they're developing curiosity on their surrounding at a young age.
That's a good start so that she will not be afraid of the dentist since we want our child to develop clean oral hygiene to have them clean and white teeth.