Eat vegetables regularly , drink enough water and use your brain intensively (read, write, or, the hardest one and the most healthier , dedicate 2 hours a day for learning something new).
And whenever the hate feeling comes at you regarding the gym, keep telling yourself that you do this for your child.
I am personally more involved if I do something for someone I care, but I think this depends on the personality of each and one of us.
Take care, stay healthy!
This is awesome advice. You rock. :)