Feel guilty if I'm not interacting with the kids

I'm a single parent to a 4 and 6 year old. My ex has main custody because of my mental health. Essentially I don't feel I can parent to a sufficient standard. No one understands how a mother can hand over custody of her kids to her ex, but I did.

My confidence in parenting is nil. When I have my kids with me, unless I am actively interacting with them, I feel crippled with guilt. So in my mind: unless I'm stimulating them, I'm neglecting them.

This means that I find parenting extremely stressful due to not having enough ideas of how to keep them entertained. I do parks, museums, cinema, but because of my anxiety I find these stressful too!

Does anyone identify with this? I feel quite the freak