First of all, your family are a bunch of dicks. How dare they devalue you like that. They sound toxic af! Your ex sounds like a prick as well. All of them are talking bollocks.
Secondly, I don’t think you should be looking to date atm. I think with your self esteem being so low you’d be an easy target for abusive men. Instead, you should build up your self esteem before you start dating. Start by getting yourself a fresh new notebook. Take some time to sit quietly when the children are in bed and write down as many things as you can think of that are good about you as a person. It would be anything. Examples could be,
I’m a good mum.
I am strong enough to raise my children singlehandedly.
I have a good heart.
I have a lot of love to give.
I am kind.
I have good hair.
I am cute.
I am a good friend.
I am fun, etc.
Try and write 5 good things about yourself to start with. Add at least 1 thing to your list every day. Read this list back to yourself every day, preferably when you first wake up and just before bed. It’s retraining you to appreciate how awesome you are. It’s training you to see all your good points and become self aware. It will build your confidence and self esteem. Also, read about self esteem. Here’s a book to get you started
https://ia600704.us.archive.org/31/items/TheSixPillarsOfSelfEsteem_201811/The-Six-Pillars-of-Self-Esteem.pdf
Once you’re feeling better about yourselfc then think about dating. However, reading between the lines it’s seems you’ve grown up around a less than supportive family and your ex sounds abusive, so you might benefit from doing the freedom programme to learn about red flags when you do enter the dating pool.
https://www.freedomprogramme.co.uk
This book might also be helpful so that you can learn bad behaviours and spot red flags.
https://www.docdroid.net/2fZmz40/why-does-he-do-that-pdf
There is nothing wrong with you so you will find a man who will love you and love your children too. I was a single mum and I’m now happily married. Of course there will be arseholes out there who might try to take advantage of you but take your time getting to know someone. Don’t get too serious soo quickly. Keep it fun, you set the pace and don’t chase after any man. A man who is into you will prioritise you, will accept you as you are, will love you as you are and will be thrilled to have you in his life.