The key thing is, that you don't have to ask anyone else about what you spend. There is no right answer and you definitely don't need vindication from a bunch of strangers on the Internet. Have confidence in yourself - as a Mum, whatever you decide is absolutely fine and your DC will have a lovely Christmas.
The fact you're asking suggests you lack confidence and worry what others think. You can see from this thread that some will spend £25 (and some will certainly struggle to find £10) and some will spend £5k. Some are really keen to 'keep up with the JOneses' and see the amount of money spent as some kind of reflection on them or measure of their love for their children, and others honestly don't think about it like that or give a toss what others think.
Personally, I consider if my DC need a big ticket item at this particular point of the year. If they need a bike or a laptop then I will probably spend what is needed on that and they will get a couple of extra little bits. There will be presents from other family memebers too. If they don't need a big ticket item I will probably buy a couple of extra presents as well. I don't have a fixed budget and certainly don't think 'I must spend another £70' to reach a set amount. If there are some nice presents and a nice little pile (considering everything the family will give) and I have managed it for £50 I am pleased and have zero sense I need to spend more. It's particularly the case that small children have no idea of the price of stuff and you really don't need to spend lots for them to love what they have.
Whether we spend lots or little, it can be a great Christmas. I think it really helps to not talk about how much things cost in front of children, even if you are very aware of it and sensitive about spending yourself. Children hear you do it and they pick up the idea that more expensive is better and their value comes from how much people spend on them. It's not a nice characteristic in adults and certainly not in children, but even small ones will pick up those attitudes if we voice them. Teenagers are more aware of others and cost of items, but I have found that often the nicest teenagers are genuinely not that bothered about the cost of stuff and it's because of the way they were brought up when they were younger. Often they are from the most affluent families but they have never been told or shown their value is in how much is spent on them.
Spend what you like Op. Don't get into debt over Christmas - honestly, not worth it and your small children won't have a better Christmas for an extra £100 of presents but will suffer from a stressed parent next year who is financially struggling.