Dd almost 8, has had maybe 8 or 9 courses, two for dental infections, two lots for different wound infections; she picks at scabs, one nasty chest infection, one uti, one lot of tonsilis and a few ear infections.
Ds, 4, I've lost count. He had at least a dozen courses before he was 12 months, three lots of iv antibiotics in hdu for suspected mengitis/encephalitis, one of the admissions if turned out to be 'just' tonsillitis, another time d and v bug and one which was never got to the bottom of. Other admissions no antibotic treatment required. Lots of ear infections, chest infections and a few uti, mostly related to his genetic condition making them more likely. For a long time it was probably every other week that he needed them. Every time he has had antibiotics he has needed them, taking them has prevented hospital admissions or been potentially life saving. I don't think it has had any adverse effects on him, other medication comes into play for him to which are much more likely to have an adverse effect but are needed, other than needing lots of thrush nappy rash treatment he otherwise wouldn't have needed.
My sister and I both has lots of antibiotics as children. She was prone to tonslitis until her tonsilis were removed in her early teens. I had years and years of almost constant ear infections and almost 5 years treatment on a very low does for bad acne as it was the only thing that kept it under control. Both now healthy adults who are rarely ill.