(Budapest - Zagreb - Ljubljana) are suitable for family?

Those are all very nice cities.

Budapest feels the largest; its sights are scattered, so you'll be using the Metro and trams to move around. It has a zoo that's easy to reach by Metro.

Zagreb's historic area is more compact but is on two levels. You'll probably want to use a bus, the funicular or a taxi to get to the upper level.

Ljubljana is smaller and easier logistically. Note that the river will be very nearby during most of your sightseeing. The dragon bridge will probably be a hit with your child

I have no experience with children, but these potential issues pop out at me:

• Budapest to Zagreb is either a 5-1/2 to 6-hour train ride (if you are prepared to depart at 6:35 AM, 3:35 PM or 6:53 PM) or an interminable 11+ hour slog. Flixbus might be faster and/or offer more attractive departure times. That train trip is so long that by the time you deal with hotels at both ends of the trip you'll have lost about a whole day (over 7 hours anyway).

• Budapest has the most things to do, yet you're giving it the least time since your arrival day won't be very usable due to jetlag. I'd add a day to Budapest. Probably would take it from Ljubljana since the trip there from Zagreb is pretty short, so you'll still have half your arrival day to work with. However, this depends on your specific plans in each city.

Thanks for sharing

Any another ideas