It's some sort of acacia, but I am not sure which. Nilotica?
Looks more like Acacia dealbata to me - the individual leaflets are a little long to be Acacia nilotica, but seeing the flowers would confirm one way or the other. Acacia nilotica produces individual, yellow, ball shaped flowers, whereas A. dealbata produces much smaller, ball-shaped flowers held in clusters. Many Acacia do not have leaves like the one in your photo does, having instead lots of thorns or modified petioles instead. That narrows the range of which one this might be, but seeing flowers would have been helpful. Some varieties of Acacia featured here https://www.thespruce.com/twenty-species-acacia-trees-and-shrubs-3269672
Unfortunately there are more species of acacia than you could shake a stick at. A lot more detail than fuzzy photos of seedlings will be required to narrow down an identification. It will probably be some time before your specimens produce a flower; and it is the flower and other characteristics of maturity that will be needed.
One thing to do is to look up at the surrounding mature trees. Acacias produce lots of seed and put up volunteer seedlings from those mature specimens close by. Adding photos or descriptions of the acacias found there might give you some strong evidence to get closer to a working identification.