Sampling with replacement.  Harsh, but just RNG.  Bery bad luck,  if he only had 3 sacred there should be no expectation of getting a leggo,  but back-to-back same epic is harsh, but hardly impossible.

He was not expecting a Lego never said he was, The issue was getting the same epic back to back and with only 2 Sacreds not 3. The RNG of this happening never should happen. The Code itself would be easy to write and add and it should already be in place. 

1. You all need to stop taking the game so seriously. Lighten up. :) 

2. Duplicate epics are actually really useful to set up as faction guardians, to give your champions overall boosted stats that can really help your progression. Even when your faction gurdians are full you can use duplicates as 4* food to level up other champs to 6* faster.

Duplicate champions are normal for all these types of RPG/Hero Collector games - the difference is that in Raid these dupes can actually be put to good use to help your account. 

Honestly, he's got something useful out of this, whether that is recognized or not. 

Also, in common with all these types of games, any expectations before summoning need to be as low as possible. In fact, as your account progresses, the best way to look on summons is as just a way of getting points in fusions and events, rather than because you want/expect to get a good champion. Then if you do get something good it's a wonderful surprise.

You seem to have missed the point.  My first statement eas 'sampling with replacement.'  That means that after the first sample, you place it back in the population.  The next pull at this point would jusy as likely be a tepeat of the first pull as any other possibilly.

say you place 100 ping pong balled numberEd 1-100 in a bag.  Any ball has a 1% chance of being pulled.  If you pull no50, then replace it, it's just as likely to pull no50 on the next sample as it was in the first sample.

with a population of 100, you should expect to pull back-to-back dups 1% of the time .

im not sure way anyone would rationalize that this should never happen?

Your son learned a valuable lesson about gambling, odds and probabilities.  This is a teaching moment for you. Instead of teaching him to be a victim teach him about reality.   Its better for him to learn this here, than in some back room poker game where he loses a full week's paycheck.