Hi Soccerbrandon,
So in order to do unit conversion in this situation, it is best to first convert kg into g and then g into mg. The conversion rates are easy to remember individually for both of them.
There are 1000 g in 1 kg.
There are 1000 mg in 1 g.
So lets use 25 kg as an example:
25 kg times

gives 25000 g in 25 kg.
25000 g times

gives 25000000mg in 25000g.
This gives us the answer that 25000000mg is equal to 25kg.
Hope it helps!!