DP moved in after 10 months, I already had DS, he has no children. It was way too soon and I wish we'd waited longer. We're still together and things are great :) but have been rocky and I think it's been due to blurring the boundaries between a "serious, I really like you and want to be a partner to you, but don't feel ready for marriage yet" relationship where you don't live together, and then a full-on stepfamily situation, the hardest part is that there's no in between so you kind of have to make an in between.
He also moved in with me straight from his parents' house and I think what we should have done was the original plan where he was going to rent his own place for around 6-12 months, and we'd take turns where he'd stay here for a weekend at a time or me and DS would go and stay at his house, slowly increasing the time until we felt at home in both places, and then we'd look for somewhere to rent together.
My advice would be don't do it because you really really like being with the person and don't want to be apart from them, because that's a hormonal/new relationship feeling and doesn't translate well to long term happiness. (In short, it's based mainly on easy access to sex ) Instead if you both have your own space but you can still see each other, stay over at each others' houses etc, you can build up to the point where you're making future plans together and that's when you're probably ready to move in together.
If you don't have children then it's more risk free to move in together sooner because you can have a not-marriage-serious, but living together stage which is more about working out how you fit together, and if you split up then it's sad, but you only have stuff to divide up and move. With children you don't get that, as soon as you move in that means that it IS pretty much as serious as marriage, because it would have the same impact on the children if you were to split up, so you need to take it a lot more slowly. Wait until you feel ready and then wait another 6 months.