There's a good few hills and walks :
- Lady Mary's Walk at Crieff - flat by the river. I've seen otter and beaver there.... Google to find route map.
- Easy hill one is Kinnoul Hill above Perth. Easy walk from car park and stunning views. Maps at car park.
- Devils / Deils Cauldron at back of Crieff is great walk, big waterfalls after the rain. Go up the river, back down very peaceful road.
- more challenging but still pretty good is Crieff Knock from the Crieff Hydro hotel. Park on the street just short of hotel, or drive past it to find parking. Maps at car park.
- there's some proper big mountains, mine were wandering them at age 4 or so, but depends how far yours will walk...
Crieff has some lovely shops and cafes. Macrosty Park is a great play park. Distillery has a visitors centre, but both food and whisky is expensive. Drive further up from distillery to Loch Turret Dam for a really, really great view of what feels like proper Highlands.
Comrie Croft has great cafe and shop, you can hire bikes (or take your own) and take to the bike trails. The bike play park is great for little ones. You do need some skills on a bike though.
Comrie has some lovely craft shops and cafes, nice walks, skate park for kids.
Stirling - Wallace Monument is spectacular (cost) and the Castle too. I suggest a walk around the castle area, including the spectacular burial ground area, as it's free and more engaging that the castle for kids. Also see Kings Park - great play park, skate park and walks with stunning views.
Dunblane has a great atmosphere, nice to wander around, couple of great cafes, and one of the best play parks anywhere at the Laighills next to the river. Park at the Cathedral and walk one way for Cathedral, Dunblane Museum, Leighton Library and High Street, other way along the river under the viaduct to the beautiful Laighhills park...
North of Perth is Dunkeld. Everything there from great wee shops and superb bakery, to riverside walks and play park, The Hermitage just outside town is stunning and famous waterfall with a surprise. Well worth a day out IMO.
If you want to find some 'big mountains' but not head up them, find Sma' Glen. Park at Newton Bridge and take the farm/estate road up the glen on foot. There's a bothy (the old School House) that's a great picnic spot a mile or so up the glen.
Happy to help with more suggestions if you want....