For quite a while I've been having my (now) 3-1/2 year old daughter help me feed the fish in her 10 gallon tank... we refer to it as her job, and it's very important that she helps me with it and does it right. She thinks it's great, and it's done a good job of keeping her from getting too curious or otherwise "attacking" the tank. Granted, 20 months and 3 years is a big difference, but I think you're doing right. I'd rather teach my daughter what can and should be done than prevent her from helping or learning.
the granddaughter. . .well, that's what granddaughters do. especially at 20 months old. the husband, on the other hand. . . . he needs a beating. he should know better.
Thanks everyone for support, all seems well with the tank now, fish seem happy and water keeping crystal clear. As for the family, well I dont think they will let Maddy anywhere near it unless I'm there. Someone did suggest I get some fine netting to go over the top. Perhaps that would save the remote controls, mobile phones etc!!!