I know that kids would be able to go through, but a breeder I talked to said that they wouldn't want to be away from their moms, so they wouldn't get out.
You would be looking at a minimum of 4 feet with a hot wire running above that, But you would probably need 5 foot panels.
My big boers have a hard time jumping 2 feet, but our more agile nubian crosses can easily clear 3 and 4 feet and are a bit more of a fencing challenge combared to the boers.
I know Nigerians can be very good jumpers from reading information on here.
My Nigerians have never tried to jump a fence. But they sure do look for the holes to crawl out under. Yes there are jumpers but I know a lot of Nigerian breeders and their problems aren't jumping. I have a 4 foot no climb woven wire horse fence and have never had one jump over it. No electric either.
My nigerians that I used to have could fit through the squares on the cattle panels at the age of 6 months. It didn't look like they could fit, but as soon as they got their head through the rest of the body wiggled through. I agree with the bottom section of your fencing being the part you secure the best. My 3 Nigerians never tried to jump but they sure could find tiny little dips in the ground to make their way under the fence or through cracks along buildings. They were escape artists.