Antibiotics

Sooo kind of long story: I babysit for a living. I also have two kids. So my 2 year old got diagnosed with strep on Thursday, he's been on amoxicillin since.. My 6 year old was diagnosed last night and tonight will be on amoxicillin for 24 hours. I haven't watched the kids today just in case. Now I guess one of the kids I watched got diagnosed with strep and will be on antibiotics, but her other son hasn't gotten it (yet)... If he does get it and it shows up tomorrow & im watching them, can my kids get it again or no cause they're on antibiotics.