Locking the panel of a PA300 (Havian 30)?

[RayDF]

I share a Havian 30 with my one year old grandson and he tends to go all crazy with the unit's myriad and highly attractive buttons instead of focusing on the piano keys, as I would want.

I wonder if there is some way in which I could "lock" this Havian 30's control panel, so that no function at all would be active? (Except for the piano voice, of course.) This will allow my grandson to focus on the actual piano, instead of glitzy stuff. I looked around the manual but found nothing. (By the way, I presume that the Havian 30's software is the same as the PA300.)

Thanks in advance for your help!