You can try.
When you say the other chick is a lot bigger do you mean older or bigger as bantams vs standard chicks? If the bigger means older you have very little chance of success. The hens bond within hours of birth and try me they can count. I am always amazed with my hens (I let the hens do all the brooding) can determine which chicks are theirs and even if 1 of 6 is not within her range call that chick or rescue it.
I have had success with this especially with my good bantam moms.Putting purchased chicks under the bantam but must be within a day or two. I have also had terrible results. I have the following suggestions for success.
1. Do it after dark when all are sleeping soundly.
2. If you still have some recently hatched eggs rub the contents on the new chicks.
3. Slide the new chicks under the hen. STAY with the hen and chicks for awhile. I have had hens appear to take the chicks just fine at night but kill them first thing in the morning when she realizes she has more chicks.
4. If possible have the hen where you can check on her frequently.
5. I feel pretty comfortable that I have success after a couple of days.
I have had the most success with bantam hens that have been successful been mommies before. Good luck! It is so much