You and your whole household must self-isolate at home in line with the Welsh Government self-isolation guidance: https://gov.wales/self-isolation-stay-home-guidance-households-possible-coronavirus
To reduce the risk of passing on the infection to other household members you should take actions as outlined in the guidance.
You (as key worker) can return to work:
Your household members are to self-isolate for 14 days from your symptom onset date; if they subsequently develop symptoms themselves, they must self-isolate for at least 10 days from their symptom onset and may request a test.
Further details are available in the Welsh Government self-isolation guidance:
If the ill person in the household is not showing any signs of improvement and has not already sought medical advice, visit the NHS Direct Wales website or call NHS 111. If it is a medical emergency, call 999