Check the oil after it's had time to run down.
There's an outside chance the engine was partially seized.

You didn't state if this happened for the first cold start or after he had been mowing. IF the latter, definitely do a better job of checking the oil.

not 100% sure...I know it was running - not sure how long, it stalled and you could not pull string to restart it. I cleared debree underneath...got it started but did not seam to have full power. I added some oil, then I could not pull the cord again. After 10 minutes or so i tried again and it ran fine. I will change the oil, filter and plug and keep my fingers crossed.

well it blew up. As mentioned above, oil was added and it ran fine. I bought a kit to change the oil, filter and plug. I decided to let my son use 1 more time before the maintenace since the grass was so high. Oil was full...I checked. After 10 minutes he came screaming that the side of the motor blew out an oil was everywhere....looked like aprett violent event. Not sure what happened. Perhaps the oil was low at some point or simply not changed for a few years. The funny thing was I thought my toro was going because the engine seamed quiet compared to pop's...I guess it was the other way around.

Sounds like the major damage was done during the previous mowing and it was a matter of time.

Maybe time to give the son a lesson on checking the oil BEFORE starting the engine?

One of the reasons I do mine first (besides being good practice) is it's simply easier to read the level before it's splashed all over the dip stick.
I simply can't read mine after running until I let it sit 20-30 minutes. One of the problems of clean oil!

n ot really hos fault...he's new to the game...but he will check going forward...there was a lot of illness ovetr the past year that was a distraction and to be honest I do not think the oil was changed since 09. The filter, oil and plug will be changed each spring going forward.