Our family spent four nights in the 1st, and then four nights in the 5th - both areas had their good points in terms of easy access to what we were enjoying seeing and doing. However, all three of our kids preferred the location in the 5th - we were near the Luxembourg Gardens, and lots of shops and sights that were interesting to them. The 1st was close to the Louvre, Tuileries, etc., but for just wandering around, we all preferred the vibe around the 5th and 6th arrondissements. If you need a hotel rec, we stayed in the Hotel Excelsior Latin on Rue Cujas in the 5th, and they had several room setups that were good for families. Ours had two rooms, separated by a wall but not a door. There was AC, and the beds were really comfortable, and decor recently updated.
Overall the feel around the 1st seemed more upscale and full of shops we didn't need - while being in the Latin Quarter (especially during the summer sales - lucky us) was more fun for us.
Have a great time!