Will this do for girls as well? They’re out of stock at the moment. The boy design is my only option right now.

Yes. The absorbent core in our pants is designed to give higher absorbency where it’s needed most – at the front for boys and in the middle for girls. It’s OK for a girl to use the version for boys because the absorbency will meet her needs. However, we do not recommend that boys use the version for girls as there would not be enough absorbency where it is most needed.

Pampers - what's the different between the old (earlier than April'ish 2018) and the new (current) version of these?

The packages I've been receiving aren't the new ones anyway, though they still come with the higher price. I've been receiving packages (several) with Pampers Rewards codes that expired in 2017.