Welcome to the Forum! Great way to spend time with the kids! I think you'll be very pleased with the Ace 250. I've read nothing but good about them! We'll be waiting for pictures of your first finds! HH 8)
Congrat Frog, and welcome to the best hobby on Earth! You and your kids are going to have a lot of fun with your ACE250. It's a great machine - very sensitive and lightweight. My 9 year old daughter can handle it for a long time before tiring. Good luck, I hope to see you posting some great finds soon!
I think you'll enjoy the Ace. One bit of advice... Crank the sensitivity down to about 4 notches at first and you'll do fine. It doesn't mention anything in the little book about getting false signals at higher settings. Over time you may be able to crank it back up a little.