When in doubt call their parents or your parents up, get some real life help not just random internet help. That said, each child is different in what triggers and calms them. Check the basic three, hungry, shitty diaper (though 3 year old should be potty trained), sleepy. Also don't say Mommy is gone, like she fucking died or something, say where Mommy went and why and when she'll be back. Don't pat a child on the head like a dog unless you want to be bitten like one. Skin-ship with strangers is bad touch. Honestly, if you don't see these kids at all your basically a stranger to them. Anime figures are expensive choking hazards, not toys. Jesus man, did your sister not give you any instructions or leave any real toys with you? Do your neighbors have children? Maybe call them and ask for help if you know them well. I feel like this is a fake post, cause really how have you spent 3 years with out being alone with this child even once? Just call their MOM now and put her on the phone to the child. Be prepared for her to throw it.
He was crying maybe not because of separation anxiety, but because he is unfamiliar with his environment (assuming that they're in your house). Try to reassure him and tell him about the situation. But do not expect him to believe you. Reasoning is useless on him, because at that age he's still unable to think logically. Just… try not to lie. (^^) Three year olds throw tantrums. That's their nature. Just let him cry. I know this is trying to your patience, but he'll get more defiant and cry more if you will try to appease him. The best thing you can do is to ignore him and wait for him to calm down. Let him be the first to approach you. If you will try to coax him to eat, he'll just refuse it even if he is dying from hunger. I don't have actual experience myself in babysitting. These are all my observations on how my aunts and cousin discipline their children. Good luck!
Exorcise him. 90% chance is the devil in this kid. Now, seriously: Just let him cry? I don't see any other solution for the problem... yeah, I'm bad with kids...
@Sami-IB-Med This thread was posted this morning, so how did things go? Did he calm down in the end? Do you have the two for more than one day? If you still want tips, how old are they? It's important because what would work on a 3 year old and a 10 year old are different.
now I see why I like to respond to you, I think you are funny lol yeah let him cry, he will understand when he is a big boy
My honest advice... smack him in the head, and make sure it hits the wall sideways! *BAM* Problem solved... you handled the threat perfectly, and now you just need to call the mother that her son is dead, but don't worry, there's a discount of 1 coffin, child-sized exclusive, and you can get it for free so, slam the child into the wall like you mean it!
Just a 3 year old kid, even if you do a meh job, it's just one day, so it won't matter in the long run like some over thinkers tend to believe so no stress. Maybe put on some childrens show, anime or one of those youtube vids - not like it'll comprehend much at that stage if you're lazy. Otherwise, read to it or play with some toys n shit.