Estava brisando...

Slangy/colloquial expressions - mostly from southeast region this time, in these Internet times, many people could use across Brazill, you never know!

I was "thought-dreaming" about names to my baby in a distant future.
(eu) Estava brisando sobre nomes de bebês para meu bebê/meu filho. (poderia para a frase aqui, já faria sentido).

They were two young people, giving free rein to imagination, making scenarios in their had and having fun.

"Brisar" aqui é uma espécie de 'daydreaming', but not in a pejorative way. It's actually a "rehearse the future", explore scenarios in your heard, or even imagine things without necessarily having to make sense (child playing, sort of).
"Viajar" is also stands for "brisar" in some cases.
In the case of the baby names you could think/fantasize of unconventional names, names of products, etc, or just think seriously about a name.

Cf. Como dizer "Viajar (sentido figurado) " em inglês