Be straightforward about this one: Jakarta is hard work with elderly parents or small children, and the difficulty is not the sights, it is getting between them.
The good news is narrow but real. The MRT North-South Line is a modern build — air-conditioned, level boarding through platform screen doors, priority seating that people genuinely respect, and step-free access at the stations. If the places you want fall along that one corridor between Lebak Bulus and Bundaran HI, a day can be easy. It is one line and thirteen stations, though, so most days will not.
Everything outside that is difficult. Sidewalks are broken, blocked by parked motorbikes and food carts, interrupted by missing drain covers, or simply absent, and pushing a stroller or a wheelchair along a normal Jakarta street is a genuine struggle rather than an inconvenience. Crossing a major road often means a pedestrian overpass with two flights of stairs and no lift. TransJakarta's bus network is excellent and extensive, but its stations sit in the middle of the road and you usually reach them by exactly those footbridges — the bus is accessible, the way in often is not. The Commuterline gets very crowded at peak and station design varies a lot by age.
Two environmental factors matter more than they would elsewhere. Air quality in Jakarta is frequently poor and periodically ranks among the worst of any major city, so if anyone in your party has asthma, COPD or a heart condition, check the daily index the way you would check the weather and keep them indoors on bad days. And the traffic is genuinely punishing: a ten-kilometre trip can take an hour, so two commitments in one day across the city will exhaust an older traveller and achieve nothing. Plan fewer stops and stay longer at each.
What actually works: Grab or Gojek cars door to door rather than any attempt at multi-leg public transport; the big malls — Grand Indonesia, Plaza Indonesia, Pacific Place — as air-conditioned bases with lifts, clean toilets, prayer rooms and nursing rooms; and a hotel with a pool so children have somewhere to burn off the afternoon. As a Muslim-majority country, halal is the default and prayer facilities are everywhere, which removes a planning problem for Muslim families from the GTA. One last practical point: Jakarta is eleven hours ahead of Toronto in summer and at least one connection away, so build in a recovery day at the start. Set against all of it, Indonesians are exceptionally warm towards visiting elderly people and children, and you will find strangers helping you up stairs before you have thought to ask.