How would you address this invitation envelope?!

[Wibblewobbles]

I'm sending a kids birthday party invitation in the post, the invite is to the three kids. On the invitation itself it just says:

Dear Emily, Holly and Toby,

you are invited blah blah blah...

But I don't know how to address the envelope. The parents are unmarried women and I think one of the kids has a different surname from the other two. (The parents have different surnames.)

For simplicity can I just address it to one of the mums (the one I'm closest to) even though the invite itself is really for the kids?

I'd purchase the kids names on the envelope.

I'd just address it to "Emily, Holly and Toby". It's not formal, I agree - but it's for kids and it gets round any awkwardness. I've resorted to this with some adults where there are multiple surnames as the informality is unlikely to offend anyone!

Yeah put the kids names on it, I do - mostly because I don't know the parents names anyway

I'd just put Emily, Holly and Toby too. It really doesn't need to be formal.

Okay, you think that'll look okay with the address underneath? They're not going to be hand delivered. I know I'm overthinking this but fancied having the MN verdict!