Hi Damien, sorry to hear of your diagnosis but welcome to the group.
Depending on the location of your tumor/what type of surgery you have, your speech may not be affected too badly. I had an SCC tongue and underwent a partial glossectomy with a flap reconstruction (used a bit of my forearm skin to rebuild the missing bit) in December and I was able to speak after a week. I have a bit of a lisp now but that's about it.
Try not to worry too much until you have a surgical plan and know what to expect! The waiting for answers is the worst part.
In terms of breaking the news like others said your kids are old enough to understand. Sounds like you have a beautiful family! In my case, I had a nonhealing lesion on my tongue and I had it biopsied but waited until I met with the ENT surgeon and knew what was ahead of me before telling my family, it's easier if you have answers to the inevitable questions they will all have.
Good luck! We are here cheering you on, don't hesitate to reach out with any questions!