Telling the kids creatively!

Hi All,
I am expecting my first with my partner, who's two kids from a previous relationship live with us. We know the kids will be over the moon, but I don't just want to tell them, I want to tell them in a really cool way (I told my partner in a really quirky creative way too). The kids mother has already given them a younger sibling with her new partner, so they are already big sisters, which means I can't do the big sis shirts or anything without implying he isn't part of their family (the last thing I want to do). Any inspiration would be greatly appreciated. Thanks in advance