Interrail Europe travel advice

Hello,

Next summer I am hoping to interrail with my 7 & 9 yr old (having done research and rejected doing a road trip with either tent or caravan).
so having decided on the mode of transport I now need to decide where to stop. Europe is a BIG place with so many interesting places. I plotted a circular route using main cities (such as Zurich, Venice, Vienna, Prague, Warsaw, Budapest) but now am wondering if I would be better off (and cheaper) sticking to the smaller destinations such as Verona. The only one that is non-negotiable is Budapest as I've always wanted to go.
We've got a month and I thought I would buy the 10 travel days a month interrail pass (which is always going to end up cheaper than point to point for me as the kids go free but I do understand there maybe reservation fees on top of this for some trains). It doesn't have to be circular as I'm happy to fly home from the last place but the starting place has to be Paris.

I know there are people on here who have interrailed with children and I would love to hear your suggestions about where you went, what you did and what you enjoyed/hated.

TIA and looking forward to hearing what you guys have done.