This was me after my second baby was born. I knew I was 'wonky', my logical brain would argue with my illogical thoughts. But i struggled to overcome the intense urge to sterilise everything and my hand were cracked and bleeding from washing them every few minutes.
Fast forward 20 years and I do have good control of my fear of contamination, it rears itself if I'm very tired and anxious but I can squash it usually.
My fears seem to be the new normal with Covid!
I was put on fluoxetine for a year which helped 20 years ago.
Exposure has helped since.
Find a place you know is safe.
Say for instance your lounge.
Go through in your head the possible risks this room could pose to your child with regards to your need to sanitise.
Then take one example and think through this risk.
When this particular thing happens, do not rush to rectify it. Take some deep breaths and count to say 10.
Then reevaluate how you feel about the threat.
If you can, count to 10 again.
Repeat.
The idea is not to rush to sanitise. This only reinforces your need to do it as afterwards the relief you feel is the reinforcement to continue with this behaviour. You are trying to break this pattern.
It's uncomfortable. The key is to think through the things that make you feel uncomfortable. Then you can distinguish between what really needs cleaning and what is satisfying your need to sanitise.
Some things will need sanitising, for example hand washing after using the toilet or before eating. But logically, not much else inside your home.
Can you make an appointment to speak to your GP. You might need something to help your anxiety to get things moving in the right direction.