Chantal,
to IIS.
I second Wavytone's suggestion of a 60mm to 80mm refractor over a dob.
By the ages of your kids, they will struggle with a dob, including a table-top set up. Dobs are great, don't get me wrong - heck, I build them too.
I too have kids, and have had dozens upon dozens of experiences with other kids too, big and small, with my scopes. At their age, the effort of moving such an instrument can be too much for them, and the mental gymnastics can prove overwhelming to move a dob. Get a smaller refractor to start will make for an easier instrument for them to handle. And these small instruments are still very capable.
You will see amazing detail on the Moon (not just thousands of craters, but also lava flows, valleys and amazing shadow play), the rings of Saturn and the moons of Jupiter, and many, many dozens of deep sky objects. You won't see the arms of spiral galaxies, be it with a small refractor or a larger dob - you need to get into the realm of 12" dobs and bigger for that! And even then it also won't look anything like the photos we see.
If your youngest was 10, then I would suggest a dob. But your kids are really too little for a dob. Even a table top one. I made a few for my kids too, including a table top one, and it took my now 10 year old son quite some time to come to grips with how to move it and find what he wanted in the scope. It is surprisingly an awkward exercise. My little 2" refractor on the other hand, they mastered it straight away. They've been around scopes all their lives too, and have had more than just a couple of times to handle scopes with me. It is a tricky skill to learn for a little one.
Forget goto scopes for now. Not necessary and way too complex for your needs right now. A smart phone app, like Sky Safari, is a great tool to help find stuff in the sky. The basic Sky Safari app is free too I believe.
Alex.