Welcome and thanks for sharing your story.
I think it's very right to see your GP and talk about your challenge. When you feel mentally not ready to go back to work, maybe it's better to extend your mat leave a bit. With your GP's letter and your explanation, your company will understand and support you.
You need emotional support, talk to your family and best friends, trust me they won't feel you're bringing trouble, they will be more than happy to help.
As you've been paying so much attention to your kids, sometimes you need to move your focus back to yourself, which means, having a quality daily life, eating healthy food, doing exercise in nature, having enough sleep, finding your hobbies back, enjoying small moments, etc.
Everything will be better.