At Last: The Actual Rules to Playing Pisha-Paisha as appearing on DoctorDad.com  and kindly researched and submitted by Sonia Pressman Fuentes.

Pisha-Paisha:

A card game that requires some addition skills great for young kids learning to add. This game was taught to doctordad by Jane and Michele's great-grandfather.
Start with a deck of cards. Deal 4 to each player and 4 face up in the middle. Each player takes a turn by making one of several moves including:
1) Matching a card from the face up pile and taking the pair.
2)Adding two or more cards face value together to equal a card you have in your hand and picking up the group . For example, there is a 3 and a 5 face up and you have an 8 in your hand. Then you can say "building 8s" and take the 3 and the 5 with the eight.
You cannot build past ten (no royals can be used to build). You can build for more then one round, for example if you have a 2 and a seven there is a 5 out face up you can place the 2 on the 5 and say "building sevens." On your next turn, you can pick up with the seven the 5 and 2.
3) Playing a card face up on the table when you cannot take a card match or build.
The game continues by dealing another four cards to each player after the last four have been played. The game ends when all the cards have been dealt and played. The last person to make a match or take a building pile gets that remaining face up cards. The winner is the one with the most cards at the end.
Alternative games include assigning points to certain cards and counting the points. Each ace one point, the most spades one point, the good ten (10 of diamonds) one point, total cards two points and the good two (two of spades) one point. the player with the most points wins.
Math plus version: allow subtraction and addition to "build" to a given match (harder than it sounds.)