The joys of waterbottles!

I've had a waterbottle forever - and forever forgot to use it.
Recently, I've been awaken to the toasty joyfulness of the water bottle.  That rather ugly malleable plastic bottle with, in my case, a simple red fleece cover; filled with deliciously hot water to keeps one's toes beautifully warm.  And as everyone knows, when one's feet are warm, the rest of the body feels warm too.

It has turned decidedly chilly - not freezing, no, that implies a dry, crisp cold, no this is the wet damp chill that penetrates to the bone and causes a house to feel unloved and whatever the oppostite of homely is.  During the day Rye and me are out mostly and once home, cooking tends to add some warmth to my little house, certainly enough until Rye goes to bed and I either retire to snuggle under my duvet or lounge on the sofa with blankets and that delightful invention, the waterbottle.   This little waterbottle, I reckon, is saving me a pretty penny, tonight I almost put the heating on, yet splash some hot water into the bottle, cover it up with the fleece, laze back on the sofa, feet up on the pouffe with a blanket over my legs and I feel very toasty indeed - ok, the whiskey laced coffee might have something to do with it too ;-)

Should I buy Rye one?  I'm not sure.  I have in mind a cuddly bear type waterbottle cover that Rye can snuggle up to and it's tummy raidating a delightful warmth.   I think it's something he would like, but is a waterbottle a good idea for a 3yr old - I worry he could get burned if I misjudge how hot the water should be, and burns on littleys are far more serious than on an adult, because littley's have less surface area of skin.  I wonder if there is an age limit, I will have to google in a moment.