It's all about balance and letting other people help you! I returned to work as a teacher when my daughter was only 3.5 months old, and I was actually more ready to get back than I thought I'd be. I did have my moments, and I still miss her every day when I'm at work, but it is very fulfilling to have a purpose beyond being a mother. I've found that it makes me feel more proud to be a mom because I am a bit more "well-rounded". What I found the hardest was juggling it all, and I still am working on that! Getting a good system and schedule that works for all of you is essential. Also, take some time just for yourself every day if you can, and carve out time with your kids on the weekends that isn't interrupted by phone calls, cleaning, etc. It's tough sometimes, and I feel some days that I'm just running errands all weekend to prepare for the next work week, but I'm trying to let some of that go and do what I can do! Spending time with your kids is the thing that will recharge your batteries.
My husband is great at helping out with house chores during the week, and he takes care of the baby equally, so that has also made it manageable for me. Just remember - you are not a bad mother for working and being "away" from your little one, and with one in school, that will hopefully make it a bit easier. Enjoy the adult time at work! :)