We are having our vacation in Osaka from Dec 5 to 11. So far, we have only planned 1 day for Universal Studios, and another day to visit Nara (Deer park , Todaiji temple and Naramachi districtApart from Kyoto and Tokyo (as we have already been there few years back), any other recommended day trips which is child-friendly? My kids are aged 4 and 6Thanks in advance

I'm afraid I can't speak to the interests of your children, but would encourage you to consult japan-guide.com. Here's the page on Osaka:
https://www.japan-guide.com/e/e2157.html

This is great for families with kids in Japan; lots of good recommendations:

https://bestlivingjapan.com/osaka-one-day-itinerary/

Visit Pokemon Cafe in Pokemon Center Osaka. I think your kids will love their cute Pokemon themed foods and Pikachu mascot show during your dining.