How do you get engaged..because I'm on level 11 and they are moved in with..

You have to wait in till you get a engage goal

Make sure the relationship Bar between your two Sims is full on partner. Then make sure ou are on the get engaged goal.

Keep your couple being romantic and/or whoo-hooing and their relationship level will increase eventually giving you the "get married" option.

Okay now that I've explained that part, let's go to getting engaged, married and have a baby step by step. Before you even start you have to be on level 10. If so , make sure your Sims aren't living together officially( you will know this if your sim has carried it's partners last name) if they are living with each other officially then pick two other sims that have partner statues and aren't officially living together. To get engaged you have to wait for the goal first, it sucks but the upside is the game rewards you with the life points. Okay let's go to get engaged, married and have a baby step by step. Before you even start you have to be on level 10. If so , make sure your sims aren't living together officially( you will know this if your sim has carried it's partners last name) if they are living with each other officially then pick two other sims that have partner statues and aren't officially living together. To get engaged you have to wait for the goal first, it sucks but the upside is the game rewards you with the life points in order to complete this task( which by the way is 25 life points but this will be the only time it will happen.) 
Now if you are on the "get engaged goal" this is what you need to do.
1) don't pop the question right away.
2) make sure all your Sims and it's partners needs are at max level ( it helps so you will get a positive response) if not get them at a max.
3) select your Sims partner, when the action menu pops up select " be romantic" ( do this until you see " propose" on the action menu) if you already see " propose" then " be romantic" only once.
4) once you have been romantic with your sim select " propose" from the action menu. When you select " propose" you will Notice a menu that has a selection of engagement rings. ( you'll be tempted to get the cheapest one, however you will risk your dims partner to turn you down and the you will have to buy a ring all over again) pick wisely, if your Sims fiancé ( male or female) lives and expensive life, then he or she will want the most expensive ring. Choose the most expensive ring to assure your sims partner will say " yes"
5) once your Sims partner accepts, you will get a goal so you guys can move in together( you can move in before the goal, but waiting rewards you with a life point) however, if you want your sim to take her fiancé last name. Have both sims go to his house and have him ask her to move in( to make sure he does make sure the green diamond is on him) remember to get positive results make sure sims needs are at a max.
6) once you have them move in max out their relationship statues so you can finally tie the knot( woohoo a lot) 
7) to have the baby you will have to wait and get it as a goal( upside you get rewarded with the 15 life points to get your baby, the crib is on you ) 
8) once you get it as a goal, set up your nursery. Make sure your Sims needs are at a max. You will Notice your crib has a (sim +) select it and add your baby just like you would do with an Adult sim. Now all you have to do is wait a day for your baby to come. Once a day goes by select the bubble over the crib and pick your baby( you will be able to customize your baby's clothes , gender and eye color) once your done you are ready to care for your baby. 
Having trouble making baby go potty you can look for my previous entry on how to resolve this issue or go to www.supercheats.com where I go step by step on how to have you're baby use the potty my username is Jersey2315. Or you can go to asked questions were I give another user the solution.
Hope this help. 
Hope this helps

After completing a goal that requires you to make 10 Sims garden at once, there will be a new goal telling you to make two sims become partners and then propose marriage. They will give you 20 llifestyle points to buy the most expensive ring after you propose marriage. Then, you'll have to fill up the relationship Bar once more resulting in their marriage.

I have the same problem but have you moved in together try that

]Well you have to keep completing the Goals and then one of the goals is get engaged, then you can propose and then you can have Children!

I have completed all possible Goals, but 'Get Engaged' was not in the list. Now they ask me to have a baby and celebrate it's birthday, but to have a baby you should be married... So, I'm stuck...
Can anyone help me?

U can't live together before getting married so one of you're Sims will have to move out then get married then you can move in together

You have to keep completing you Goals until one of your goals say get engaged.

You have to wait till 2 Sims are partners. There will be an option that says propose. Don't pop the question right away. Keep on woo hooing and being romantic then you choose a ring. And your sim will propose to the other one. The one who is getting proposed to will either say yes or no. If you buy a nice ring and not not the cheap dinosaur ring then chances are she will say yes. Then they get engaged. Hope this helped!

I'm already at the "get engage" goal and the "propose marriage" is already available but the rings are not yet available in the market. I''m stuck on this goal and I am already at level ten.