Hah. Recently I went searching for old wallets of mine. Found .5 BTC in Blockchain and .1 in each of 3 Coinbase accounts. At the time I had created each those the BTC they contained was all worth less than a dollar. It was neat to find about $2k "in the couch", but also infuriating that I couldn't find more. I also have a locked wallet with 2.5BTC that I can't unlock (although I have John the Ripper plugging away at it) again which was worth nearly nothing at the time I made it.
So the short answer is, there is practically no quantity of Bitcoin too small to be worth properly securing it. If it's enough to be transactable (not dust) then for the love of god secure it and with luck your kids will be truly thankful that you did.
Easy enough to install on Linux there are plenty of guides. Just a few commands to grab the source and tools to build it and then compile the binaries.
Once you have that, there's a tool (python script I think) to extract the hash from the wallet.dat. Then you run it against that.
The hardest and most important part is seeding a proper word list for it to work off of. The default dictionary probably isn't going to crack it.
So the short answer is, there is practically no quantity of Bitcoin too small to be worth properly securing it. If it's enough to be transactable (not dust) then for the love of god secure it and with luck your kids will be truly thankful that you did.