There are lots of benefits to hawing a paid job, all of which have mentioned many times. With regards to you asking specifically about the benefits of full time working then I'm not sure there are any
People generally work full time because they need the money, which is the reason you have identified for you going back to work so there is no choice in the matter.
I'm sure many people would choose to work full time even if they didn't need to but I can't imagine many would choose to work full time if they didn't have to and had young children at home.
But - do go and enjoy the perks: being out the house, making friends,
being involved in social activities, learning new skills, contributing to society in some way, earning your own money, having child-free lunch breaks, setting a good example to your children, being able to contribute to the household expenses, pension, finding a new sense of identity etc etc
There are lots of benefits to working so embrace them and make the best of your new situation. Yes you will find it hard being away from your children but going back into the workforce can be a very exciting step for you and who knows what doors may open for you and where they made lead..::