If you read down the policy it seems to be quite specific as to what's permitted:

Checked baggage

Your child (between 2 and 11 years) will have the same free checked baggage allowance as you, which will vary depending on the cabin that you're travelling in.

...In addition, each infant and child, can take up to two of the following essential extras checked into the hold, even on a hand baggage only (Basic) fare:

• Fully collapsible pushchair (stroller)
• Car or booster seat
• Travel cot
• Baby back carrier

This appears to be the extent of additional items. You can take the bike but it will be counted as a checked baggage item and need to conform to to the associated dimensions and weight limits according to the checked baggage allowance for the ticket you've purchased (ie if on a Hand Baggage Only fare then you'll be charged accordingly to check the bike in).