When the weather cools, save money (and the planet) by keeping the heating lower for longer by putting your toddler in tights AND trousers. Small people spend most of their time at floor-level, which can be chilly. Popping a pair of tights under their trousers will help to keep them toasty. I wear tights under my jeans for the whole chilly season too.
Gap has these unisex, navy, teddy bear tights, with rubber grippers on the soles for safety - tights without sole grips will just lead to more falling over if you spend time in places with non-carpeted floors.
Mountain Warehouse sells these excellent Merino wool base layer leggings - for babies up to age 13! They are lightweight and soft (not scratchy like other wool types) and hardly need washing (unless there is a nappy leak if worn by toddlers). They do survive the washing machine at 40 C without shrinking. (I always do a cool wash-by-hand for Merino wool items - which isn't much of a hardship as they need washing only very rarely being naturally antibacterial and therefore not smelly - but occasionally these have ended up in the washing machine, and have survived!)