If you feel you want to explore it by all means do but prepare yourself for possible heartache in that normally there is at least 2 years between adopted children and any existing children, also if they are in foster care locally it may mean their birth parents are local and the plan may be to adopt them in a further away part of your county. Also, if they are a different race to you and your family this may be an issue. However, if you want to enquire, why not ask. But do not say anything to your children or anyone else locally, I am sure you will not.
You do not say if you are married/with a partner, how they feel or if you have spoken about it, whether you have other kids, whether you can afford to take a year or at least 6 months of adoption leave.
Please do not say all these things as it may identify you, I am just saying there is a lot to think about. Also if you have one child and adopt two more the existing child might feel a bit overwhelmed! If you already have two or more it would be fine or if you had ne and adopted one but adopting two into a home with one child is a lot of change.
Maybe this has stirred in you an interest in adoption or fostering or respite care. Whatever it is I would explore it tentatively, but with a recognition that it may well not be for these children. My interest in adoption was stirred by a 6 year old boy in Romania 25 years ago. he would be about 30 now!