We stayed at a citadines near to gare De Lyon/bastille in May with DC aged 6 and 4. They slept in twin room and we had sofa bed which was perfectly comfortable for four nights. Apartment was absolutely fine for our purposes as we hardly spent anytime there, not luxury but not completely basic either. Had a fridge and basic hob and possibly a microwave. We cooked a couple of simple meals and ate out for a few nights.
It was a 2 min walk from the nearest metro (reuilly diderot), a small supermarket across the road and two boulangeries nearby. It was easy to get around the metro and our kids enjoyed the whole trip, although they were very tired.
We got a metro ticket each which lasted for five days I think, can't remember what they were called but they were well worth it as we could use the metro whenever we felt like it and didn't need to faff around getting change.
The apartment was near to the old railway line that has been converted into a park which was nice for a walk and there was a play area about 15 mins walk along it.
We bought a batobus boat ticket so could make unlimited trips in one day on the seine. We walked up the Eiffel tower to the second level, cheap, no queues, great views and exhausting! Also went back to watch the Eiffel tower lit up at night from the other side of the river, trocadero gardens I think it's called. Kids loved it!
We also went up l'arc De triomphe which had good views as well especially of the Eiffel tower.
We did a lot of walking around the botanic gardens and from the louvre up to the l'arc 're triomphe. Also went to parc de Luxembourg which is lovely and has a good play area (you have to pay a small entrance fee) and parc de villette which was modern and unusual and a bit different. Also wandered around sacre Coeur and Notre dame and had lovely ice cream on the smallest of the islands on the seine. Also want to monmartre but wasn't massively impressed, it was also the only place we got hassled, properly hassled, by men trying to put wristbands on us in the steps up to sacre Coeur. No problems anywhere else.
All in all it was a great but exhausting trip!