I recommend the trail across Pohorje with children in the direction from Slovenj Gradec to Maribor, as we usually return to the valley in the evening, and from Maribor there are better connections to your home place than from Slovenj Gradec. It's true that if you're in excellent condition, you can do the tour in one day, but if you want to enjoy along the way, not just rush, take 3 days.
1st day (Friday)
This will be the most strenuous due to overcoming the greatest elevation differences. Bus ride to Slovenj Gradec, moderate ascent to Kremžarjev vrh, which steepens towards the top. From Kremžarjev vrh to Partizanka at Kopa follows the most strenuous part of the trail, as the path through the forest first steeply descends to the lowest point, then steeply ascends almost all the way to Kopa. Considering you'll have backpacks with quite a bit of luggage (at least a windbreaker, some clothes and water), you'll rest most often on this section. But you'll be rewarded in this area with a view of an endless sea of bushes of purple heather. From Kopa to the highest point of Pohorje - Črni vrh, you'll travel through an endless sea of blueberries and cranberries ripening just in summer time and soon after you'll find yourselves at Ribniška koča, where I recommend the first overnight.
2nd day (Saturday)
After a hearty breakfast, you'll continue on a less strenuous path to Rogla, Pesek and Klopni vrh. Along the way, you can see the beautiful Ribniško and Lovrenška lakes. At Klopni vrh I recommend the second overnight, as here you can truly rest at a quiet place. Pesek is too close to Rogla and people most often drive there by car to party in the evening hours, when tired hikers with children want rest.
3rd day (Sunday)
From Klopni vrh the path now leads to the Pohorje primeval forest and Šumik waterfall, from there without major ascents and descents to Areh and Ruška koča. From there to Mariborska koča, which is the last stop before Bellevue on Mariborsko Pohorje. If darkness and fatigue haven't overtaken you yet, from here follows the descent to Poštela and Spodnje Radvanje in Maribor. Otherwise, no one will blame you if you take the cable car down to the valley. If you were inventive, you did it yourself, or asked some acquaintance to park your car under the cable car, with which at the end of the path you can drive home, otherwise the bus will be fine too.
Finally, it's not superfluous to mention to arrange alpine cards before the trip, both for discounts on accommodations and for insurance in case of some unfortunate event. A Pohorje map won't be superfluous either, as a moment of inattention can quickly lead you far off the planned path.
Happy trails!