A single mother my 12 year old son has disability credit do I say yes to claim him and I have a 1 year old daughter click yes to claim her or can I just claim one child?

You can enter both children as dependants.

You can claim one child (either one) as an eligible dependant if you qualify. For your son, you can transfer his disability amount to you in the Dependants section. You will need to include some details for him (net income, etc.) to complete the transfer.